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Ingy döt Net 2023-07-01 11:58:00 -04:00
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---
from: http://rosettacode.org/wiki/Blum_integer

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;Definition
A positive integer '''n''' is a '''Blum integer''' if ''n = p x q'' is a semi-prime for which ''p'' and ''q'' are distinct primes congruent to 3 mod 4. In other words, ''p'' and ''q'' must be of the form 4''t'' + 3 where ''t'' is some non-negative integer.
<br>
;Example
21 is a Blum integer because it has two prime factors: 3 (= 4 x 0 + 3) and 7 (= 4 x 1 + 3).
;Task
Find and show on this page the first '''50''' Blum integers.
Also show the '''26,828'''th.
<br>
;Stretch
Find and show the '''100,000'''th, '''200,000'''th, '''300,000'''th and '''400,000'''th Blum integers.
For the first '''400,000''' Blum integers, show the percentage distribution by final decimal digit (to 3 decimal places). Clearly, such integers can only end in 1, 3, 7 or 9.
;Related task
* [[Semiprime]]
;References
* Wikipedia article [[wp:Blum_integer|Blum integer]]
* OEIS sequence [[oeis:A016105|A016105: Blum integers]]
<br>

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BEGIN # find Blum integers, semi-primes where both factors are 3 mod 4 #
# and the factors are distinct #
INT max number = 10 000 000; # maximum possible Blum we will consider #
[ 1 : max number ]INT upfc; # table of unique prime factor counts #
[ 1 : max number ]INT lpf; # table of last prime factors #
FOR i TO UPB upfc DO upfc[ i ] := 0; lpf[ i ] := 1 OD;
FOR i FROM 2 TO UPB upfc OVER 2 DO
IF upfc[ i ] = 0 THEN
FOR j FROM i + i BY i TO UPB upfc DO
upfc[ j ] +:= 1;
lpf[ j ] := i
OD
FI
OD;
# returns TRUE if n is a Blum integer, FALSE otherwise #
PROC is blum = ( INT n )BOOL:
IF n < 21 THEN FALSE # the lowest primes modulo 4 that are 3 are #
# 3 & 7, so 21 is the lowest possible number #
ELIF NOT ODD n THEN FALSE
ELSE
INT v := n;
INT f count := 0;
INT f := 3;
WHILE f <= v AND f count < 3 DO
IF v MOD f = 0 THEN
IF f MOD 4 /= 3 THEN
f count := 9 # the prime factor mod 4 isn't 3 #
ELSE
v OVERAB f;
f count +:= 1
FI;
IF v MOD f = 0 THEN
f count := 9 # f is not a distinct factor of n #
FI
FI;
f +:= 2
OD;
f count = 2
FI # is blum # ;
# show various Blum integers #
print( ( "The first 50 Blum integers:", newline ) );
INT b count := 0;
[ 0 : 9 ]INT last count := []INT( 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 )[ AT 0 ];
FOR i FROM 21 BY 4 WHILE b count < 400 000 DO
# Blum integers must be 1 modulo 4 #
IF b count < 50 THEN
IF is blum( i ) THEN
b count +:= 1;
last count[ i MOD 10 ] +:= 1;
print( ( whole( i, -4 ) ) );
IF b count MOD 10 = 0 THEN print( ( newline ) ) FI
FI
ELIF upfc[ i ] = 2 THEN
# two prime factors - could be a Blum integer #
IF lpf[ i ] MOD 4 = 3 THEN
# the last prime factor mod 4 is three #
IF upfc[ i OVER lpf[ i ] ] = 0 THEN
# and the other prime factor is unique (e.g. not 3^3) #
b count +:= 1;
last count[ i MOD 10 ] +:= 1;
IF b count = 26 828
OR b count = 100 000
OR b count = 200 000
OR b count = 300 000
OR b count = 400 000
THEN
print( ( "The ", whole( b count, -6 )
, "th Blum integer is ", whole( i, -11 )
, newline
)
)
FI
FI
FI
FI
OD;
# show some statistics of the last digits #
print( ( "For Blum integers up to ", whole( b count, 0 ), ":", newline ) );
FOR i FROM LWB last count TO UPB last count DO
IF last count[ i ] /= 0 THEN
print( ( " ", fixed( ( last count[ i ] * 100 ) / b count, -8, 3 )
, "% end with ", whole( i, 0 )
, newline
)
)
FI
OD
END

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#include <stdio.h>
#include <stdbool.h>
#include <locale.h>
int inc[8] = {4, 2, 4, 2, 4, 6, 2, 6};
bool isPrime(int n) {
if (n < 2) return false;
if (n%2 == 0) return n == 2;
if (n%3 == 0) return n == 3;
int d = 5;
while (d*d <= n) {
if (n%d == 0) return false;
d += 2;
if (n%d == 0) return false;
d += 4;
}
return true;
}
// Assumes n is odd.
int firstPrimeFactor(int n) {
if (n == 1) return 1;
if (!(n%3)) return 3;
if (!(n%5)) return 5;
for (int k = 7, i = 0; k*k <= n; ) {
if (!(n%k)) {
return k;
} else {
k += inc[i];
i = (i + 1) % 8;
}
}
return n;
}
int main() {
int i = 1, j, bc = 0, p, q;
int blum[50], counts[4] = {0}, digits[4] = {1, 3, 5, 7};
setlocale(LC_NUMERIC, "");
while (true) {
p = firstPrimeFactor(i);
if (p % 4 == 3) {
q = i / p;
if (q != p && q % 4 == 3 && isPrime(q)) {
if (bc < 50) blum[bc] = i;
++counts[i % 10 / 3];
++bc;
if (bc == 50) {
printf("First 50 Blum integers:\n");
for (j = 0; j < 50; ++j) {
printf("%3d ", blum[j]);
if (!((j+1) % 10)) printf("\n");
}
printf("\n");
} else if (bc == 26828 || !(bc % 100000)) {
printf("The %'7dth Blum integer is: %'9d\n", bc, i);
if (bc == 400000) {
printf("\n%% distribution of the first 400,000 Blum integers:\n");
for (j = 0; j < 4; ++j) {
printf(" %6.3f%% end in %d\n", counts[j]/4000.0, digits[j]);
}
break;
}
}
}
}
i += (i % 5 == 3) ? 4 : 2;
}
return 0;
}

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program BlumInteger;
{$IFDEF FPC} {$MODE DELPHI}{$Optimization ON,ALL} {$ENDIF}
{$IFDEF WINDOWS}{$APPTYPE CONSOLE}{$ENDIF}
{
// for commatize = Numb2USA(IntToStr(n))
uses
sysutils, //IntToStr
strutils; //Numb2USA
}
const
LIMIT = 10*1000*1000;// >750
type
tP4n3 = array of Uint32;
function CommaUint(n : Uint64):AnsiString;
//commatize only positive Integers
var
fromIdx,toIdx :Int32;
pRes : pChar;
Begin
str(n,result);
fromIdx := length(result);
toIdx := fromIdx-1;
if toIdx < 3 then
exit;
toIdx := 4*(toIdx DIV 3)+toIdx MOD 3 +1 ;
setlength(result,toIdx);
pRes := @result[1];
dec(pRes);
repeat
pRes[toIdx] := pRes[FromIdx];
pRes[toIdx-1] := pRes[FromIdx-1];
pRes[toIdx-2] := pRes[FromIdx-2];
pRes[toIdx-3] := ',';
dec(toIdx,4);
dec(FromIdx,3);
until FromIdx<=3;
while fromIdx>=1 do
Begin
pRes[toIdx] := pRes[FromIdx];
dec(toIdx);
dec(fromIdx);
end;
end;
procedure Sieve4n_3_Primes(Limit:Uint32;var P4n3:tP4n3);
var
sieve : array of byte;
BlPrCnt,idx,n,j: Uint32;
begin
//DIV 3 -> smallest factor of Blum Integer
n := (LIMIT DIV 3 -3) DIV 4+ 1;
setlength(sieve,n);
setlength(P4n3,n);
BlPrCnt:= 0;
idx := 0;
repeat
if sieve[idx]= 0 then
begin
n := idx*4+3;
P4n3[BlPrCnt] := n;
inc(BlPrCnt);
j := idx+n;
if j > High(sieve) then
break;
while j <= High(sieve) do
begin
sieve[j] := 1;
inc(j,n);
end;
end;
inc(idx);
until idx>High(sieve);
//collect the rest
for idx := idx+1 to High(sieve) do
if sieve[idx]=0 then
Begin
P4n3[BlPrCnt] := idx*4+3;
inc(BlPrCnt);
end;
setlength(P4n3,BlPrCnt);
setlength(sieve,0);
end;
var
BlumField : array[0..LIMIT] of boolean;
BlumPrimes : tP4n3;
EndDigit : array[0..9] of Uint32;
k : Uint64;
n,idx,j,P4n3Cnt : Uint32;
begin
Sieve4n_3_Primes(Limit,BlumPrimes);
P4n3Cnt := length(BlumPrimes);
writeln('There are ',CommaUint(P4n3Cnt),' needed primes 4*n+3 to Limit ',CommaUint(LIMIT));
dec(P4n3Cnt);
writeln;
//generate Blum-Integers
For idx := 0 to P4n3Cnt do
Begin
n := BlumPrimes[idx];
For j := idx+1 to P4n3Cnt do
Begin
k := n*BlumPrimes[j];
if k>LIMIT then
BREAK;
BlumField[k] := true;
end;
end;
writeln('First 50 Blum-Integers ');
idx :=0;
j := 0 ;
repeat
while (idx<LIMIT) AND Not(BlumField[idx]) do
inc(idx);
if idx = LIMIT then
BREAK;
if j mod 10 = 0 then
writeln;
write(idx:5);
inc(j);
inc(idx);
until j >= 50;
Writeln(#13,#10);
//count and calc and summate decimal digit
writeln(' relative occurence of digit');
writeln(' n.th |Blum-Integer|Digit: 1 3 7 9');
idx :=0;
j := 0 ;
n := 0;
k := 26828;
repeat
while (idx<LIMIT) AND Not(BlumField[idx]) do
inc(idx);
if idx = LIMIT then
BREAK;
//count last decimal digit
inc(EndDigit[idx MOD 10]);
inc(j);
if j = k then
begin
write(CommaUint(j):10,' | ',CommaUint(idx):11,'| ');
write(EndDigit[1]/j*100:7:3,'% |');
write(EndDigit[3]/j*100:7:3,'% |');
write(EndDigit[7]/j*100:7:3,'% |');
writeln(EndDigit[9]/j*100:7:3,'%');
if k < 100000 then
k := 100000
else
k += 100000;
end;
inc(idx);
until j >= 400000;
Writeln;
end.

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Dim Shared As Uinteger Prime1
Dim As Uinteger n = 3, c = 0, Prime2
Function isSemiprime(n As Uinteger) As Boolean
Dim As Uinteger d = 3, c = 0
While d*d <= n
While n Mod d = 0
If c = 2 Then Return False
n /= d
c += 1
Wend
d += 2
Wend
Prime1 = n
Return c = 1
End Function
Print "The first 50 Blum integers:"
Do
If isSemiprime(n) Then
If Prime1 Mod 4 = 3 Then
Prime2 = n / Prime1
If (Prime2 <> Prime1) And (Prime2 Mod 4 = 3) Then
c += 1
If c <= 50 Then
Print Using "####"; n;
If c Mod 10 = 0 Then Print
End If
If c >= 26828 Then
Print !"\nThe 26828th Blum integer is: " ; n
Exit Do
End If
End If
End If
End If
n += 2
Loop
Sleep

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package main
import (
"fmt"
"rcu"
)
var inc = []int{4, 2, 4, 2, 4, 6, 2, 6}
// Assumes n is odd.
func firstPrimeFactor(n int) int {
if n == 1 {
return 1
}
if n%3 == 0 {
return 3
}
if n%5 == 0 {
return 5
}
for k, i := 7, 0; k*k <= n; {
if n%k == 0 {
return k
} else {
k += inc[i]
i = (i + 1) % 8
}
}
return n
}
func main() {
blum := make([]int, 50)
bc := 0
counts := make([]int, 4)
i := 1
for {
p := firstPrimeFactor(i)
if p%4 == 3 {
q := i / p
if q != p && q%4 == 3 && rcu.IsPrime(q) {
if bc < 50 {
blum[bc] = i
}
counts[i%10/3]++
bc++
if bc == 50 {
fmt.Println("First 50 Blum integers:")
rcu.PrintTable(blum, 10, 3, false)
fmt.Println()
} else if bc == 26828 || bc%100000 == 0 {
fmt.Printf("The %7sth Blum integer is: %9s\n", rcu.Commatize(bc), rcu.Commatize(i))
if bc == 400000 {
fmt.Println("\n% distribution of the first 400,000 Blum integers:")
digits := []int{1, 3, 7, 9}
for j := 0; j < 4; j++ {
fmt.Printf(" %6.3f%% end in %d\n", float64(counts[j])/4000, digits[j])
}
return
}
}
}
}
if i%5 == 3 {
i += 4
} else {
i += 2
}
}
}

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isblum=: {{
ab=. q: y
if. 2= #ab do.
if. </ab do.
*./3=4|ab
else. 0 end.
else. 0 end.
}}"0
blumseq=: {{
r=. (#~ isblum) }.i.b=. 1e4
while. y>#r do.
r=. r, (#~ isblum) b+i.1e4
b=. b+1e4
end.
y{.r
}}

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5 10$blumseq 50
21 33 57 69 77 93 129 133 141 161
177 201 209 213 217 237 249 253 301 309
321 329 341 381 393 413 417 437 453 469
473 489 497 501 517 537 553 573 581 589
597 633 649 669 681 713 717 721 737 749
{: blumseq 26828
524273

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B=: blumseq 4e5
{:1e5{.B
2075217
{:2e5{.B
4275533
{:3e5{.B
6521629
{:4e5{.B
8802377
{:B
8802377
(~.,. 4e3 %~ #/.~) 10|B
1 25.0012
3 25.0167
7 24.9973
9 24.9847

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### Generic utilities
def lpad($len): tostring | ($len - length) as $l | (" " * $l) + .;
# tabular print
def tprint(columns; wide):
reduce _nwise(columns) as $row ("";
. + ($row|map(lpad(wide)) | join(" ")) + "\n" );
### Primes
def is_prime:
. as $n
| if ($n < 2) then false
elif ($n % 2 == 0) then $n == 2
elif ($n % 3 == 0) then $n == 3
elif ($n % 5 == 0) then $n == 5
elif ($n % 7 == 0) then $n == 7
elif ($n % 11 == 0) then $n == 11
elif ($n % 13 == 0) then $n == 13
elif ($n % 17 == 0) then $n == 17
elif ($n % 19 == 0) then $n == 19
else sqrt as $s
| 23
| until( . > $s or ($n % . == 0); . + 2)
| . > $s
end;
def primes: 2, (range(3;infinite;2) | select(is_prime));
# input: the number to be tested
def isprime($smalls):
if . < 2 then false
else sqrt as $s
| (first( $smalls[] as $p
| if . == $p then 1
elif . % $p == 0 then 0
elif $p > $s then 1
else empty
end) // null) as $result
| if $result then $result == 1
else ($smalls[-1] + 2)
| until( . > $s or ($n % . == 0); . + 2)
| . > $s
end
end;
# Assumes n is odd.
def firstPrimeFactor:
if (. == 1) then 1
elif (. % 3 == 0) then 3
elif (. % 5 == 0) then 5
else . as $n
| [4, 2, 4, 2, 4, 6, 2, 6] as $inc
| { k: 7,
i: 0 }
| ($n | sqrt) as $s
| until (.k > $s or .done;
if $n % .k == 0
then .done = true
else .k += $inc[.i]
| .i = (.i + 1) % 8
end )
| if .done then .k else $n end
end ;
### Blum integers
# Number of small primes to pre-compute
def task($numberOfSmallPrimes):
[limit($numberOfSmallPrimes; primes)] as $smalls
| { blum: [],
bc:0,
counts: { "1": 0, "3": 0, "7": 0, "9": 0 },
i: 1 }
| label $out
| foreach range(0; infinite) as $_ (.;
(.i|firstPrimeFactor) as $p
| .j = null
| if ($p % 4 == 3)
then (.i / $p) as $q
| if $q != $p and ($q % 4 == 3) and ($q | isprime($smalls))
then if (.bc < 50) then .blum[.bc] = .i else . end
| .counts[(.i % 10) | tostring] += 1
| .bc += 1
| .j = .i
else .
end
else .
end
| .i |= if (. % 5 == 3) then . + 4 else . + 2 end;
select(.j)
| if (.bc == 50)
then "First 50 Blum integers:",
(.blum | tprint(10; 3) )
elif .bc == 26828 or .bc % 1e5 == 0
then "The \(.bc) Blum integer is: \(.j)",
if .bc == 400000
then "\n% distribution of the first 400,000 Blum integers:",
((.counts|keys_unsorted[]) as $k
| " \( .counts[$k] / 4000 )% end in \($k)"),
break $out
else empty
end
else empty
end);
task(10000)

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using Formatting, Primes
function isblum(n)
pe = factor(n).pe
return length(pe) == 2 && all(p -> p[2] == 1 && p[1] % 4 == 3, pe)
end
const blum400k = @view (filter(isblum, 1:9_000_000))[1:400_000]
println("First 50 Blum integers:")
foreach(p -> print(rpad(p[2], 4), p[1] % 10 == 0 ? "\n" : ""), enumerate(blum400k[1:50]))
for idx in [26_828, 100_000, 200_000, 300_000, 400_000]
println("\nThe $(format(idx, commas = true))th Blum number is ",
format(blum400k[idx], commas = true), ".")
end
println("\n% distribution of the first 400,000 Blum integers is:")
for d in [1, 3, 7, 9]
println(lpad(round(count(x -> x % 10 == d, blum400k) / 4000, digits=3), 8), "% end in $d")
end

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import std/[strformat, tables]
func isPrime(n: Natural): bool =
## Return "true" is "n" is prime.
if n < 2: return false
if (n and 1) == 0: return n == 2
if n mod 3 == 0: return n == 3
var d = 5
var step = 2
while d * d <= n:
if n mod d == 0:
return false
inc d, step
step = 6 - step
return true
const Inc = [4, 2, 4, 2, 4, 6, 2, 6]
func firstPrimeFactor(n: Positive): int =
## Return the first prime factor.
## Assuming "n" is odd.
if n == 1: return 1
if n mod 3 == 0: return 3
if n mod 5 == 0: return 5
var k = 7
var i = 0
while k * k <= n:
if n mod k == 0:
return k
k += Inc[i]
i = (i + 1) and 7
return n
var blum: array[50, int]
var bc = 0
var counts: CountTable[int]
var n = 1
while true:
var p = n.firstPrimeFactor
if (p and 3) == 3:
let q = n div p
if q != p and (q and 3) == 3 and q.isPrime:
if bc < 50: blum[bc] = n
counts.inc(n mod 10)
inc bc
if bc == 50:
echo "First 50 Blum integers:"
for i, val in blum:
stdout.write &"{val:3}"
stdout.write if i mod 10 == 9: '\n' else: ' '
echo()
elif bc == 26828 or bc mod 100000 == 0:
echo &"The {bc:>6}th Blum integer is: {n:>7}"
if bc == 400000:
echo "\n% distribution of the first 400_000 Blum integers:"
for i in [1, 3, 7, 9]:
echo &" {counts[i]/4000:6.3f} % end in {i}"
break
n = if n mod 5 == 3: n + 4 else: n + 2

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use v5.36;
use enum <false true>;
use ntheory <is_prime gcd>;
sub comma { reverse ((reverse shift) =~ s/.{3}\K/,/gr) =~ s/^,//r }
sub table ($c, @V) { my $t = $c * (my $w = 5); ( sprintf( ('%'.$w.'d')x@V, @V) ) =~ s/.{1,$t}\K/\n/gr }
sub is_blum ($n) {
return false if $n < 2 or is_prime $n;
my $factor = find_factor($n);
my $div = int($n / $factor);
return true if is_prime($factor) && is_prime($div) && ($div != $factor) && ($factor%4 == 3) && ($div%4 == 3);
false;
}
sub find_factor ($n, $constant = 1) {
my($x, $rho, $factor) = (2, 1, 1);
while ($factor == 1) {
$rho *= 2;
my $fixed = $x;
for (0..$rho) {
$x = ( $x * $x + $constant ) % $n;
$factor = gcd(($x-$fixed), $n);
last if 1 < $factor;
}
}
$factor = find_factor($n, $constant+1) if $n == $factor;
$factor;
}
my($i, @blum, %C);
my @nth = (26828, 1e5, 2e5, 3e5, 4e5);
while (++$i) {
push @blum, $i if is_blum $i;
last if $nth[-1] == scalar @blum;
}
$C{substr $_, -1, 1}++ for @blum;
say "The first fifty Blum integers:\n" . table 10, @blum[0..49];
printf "The %7sth Blum integer: %9s\n", comma($_), comma $blum[$_-1] for @nth;
say '';
printf "$_: %6d (%.3f%%)\n", $C{$_}, 100*$C{$_}/scalar @blum for <1 3 7 9>;

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(phixonline)-->
<span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
<span style="color: #008080;">constant</span> <span style="color: #000000;">LIMIT</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1e7</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">N</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">floor</span><span style="color: #0000FF;">((</span><span style="color: #7060A8;">floor</span><span style="color: #0000FF;">(</span><span style="color: #000000;">LIMIT</span><span style="color: #0000FF;">/</span><span style="color: #000000;">3</span><span style="color: #0000FF;">)-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)/</span><span style="color: #000000;">4</span><span style="color: #0000FF;">)+</span><span style="color: #000000;">1</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">Sieve4n_3_Primes</span><span style="color: #0000FF;">()</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">sieve</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">repeat</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">,</span><span style="color: #000000;">N</span><span style="color: #0000FF;">),</span> <span style="color: #000000;">p4n3</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">idx</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #000000;">N</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sieve</span><span style="color: #0000FF;">[</span><span style="color: #000000;">idx</span><span style="color: #0000FF;">]=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">idx</span><span style="color: #0000FF;">*</span><span style="color: #000000;">4</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #000000;">p4n3</span> <span style="color: #0000FF;">&=</span> <span style="color: #000000;">n</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">idx</span><span style="color: #0000FF;">+</span><span style="color: #000000;">n</span><span style="color: #0000FF;">></span><span style="color: #000000;">N</span> <span style="color: #008080;">then</span>
<span style="color: #000080;font-style:italic;">// collect the rest</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">j</span><span style="color: #0000FF;">=</span><span style="color: #000000;">idx</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #000000;">N</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sieve</span><span style="color: #0000FF;">[</span><span style="color: #000000;">j</span><span style="color: #0000FF;">]=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">p4n3</span> <span style="color: #0000FF;">&=</span> <span style="color: #000000;">4</span><span style="color: #0000FF;">*</span><span style="color: #000000;">j</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">exit</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">j</span><span style="color: #0000FF;">=</span><span style="color: #000000;">idx</span><span style="color: #0000FF;">+</span><span style="color: #000000;">n</span> <span style="color: #008080;">to</span> <span style="color: #000000;">N</span> <span style="color: #008080;">by</span> <span style="color: #000000;">n</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">sieve</span><span style="color: #0000FF;">[</span><span style="color: #000000;">j</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">p4n3</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">p4n3</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">Sieve4n_3_Primes</span><span style="color: #0000FF;">(),</span>
<span style="color: #000000;">BlumField</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">repeat</span><span style="color: #0000FF;">(</span><span style="color: #004600;">false</span><span style="color: #0000FF;">,</span><span style="color: #000000;">LIMIT</span><span style="color: #0000FF;">),</span>
<span style="color: #000000;">Blum50</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{},</span> <span style="color: #000000;">counts</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">repeat</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">,</span><span style="color: #000000;">10</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">idx</span><span style="color: #0000FF;">,</span><span style="color: #000000;">n</span> <span style="color: #008080;">in</span> <span style="color: #000000;">p4n3</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">bj</span> <span style="color: #008080;">in</span> <span style="color: #000000;">p4n3</span> <span style="color: #008080;">from</span> <span style="color: #000000;">idx</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #004080;">atom</span> <span style="color: #000000;">k</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">n</span><span style="color: #0000FF;">*</span><span style="color: #000000;">bj</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">k</span><span style="color: #0000FF;">></span><span style="color: #000000;">LIMIT</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">BlumField</span><span style="color: #0000FF;">[</span><span style="color: #000000;">k</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">true</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">count</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">n</span><span style="color: #0000FF;">,</span><span style="color: #000000;">k</span> <span style="color: #008080;">in</span> <span style="color: #000000;">BlumField</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">k</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">count</span><span style="color: #0000FF;"><</span><span style="color: #000000;">50</span> <span style="color: #008080;">then</span> <span style="color: #000000;">Blum50</span> <span style="color: #0000FF;">&=</span> <span style="color: #000000;">n</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">counts</span><span style="color: #0000FF;">[</span><span style="color: #7060A8;">remainder</span><span style="color: #0000FF;">(</span><span style="color: #000000;">n</span><span style="color: #0000FF;">,</span><span style="color: #000000;">10</span><span style="color: #0000FF;">)]</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #000000;">count</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">count</span><span style="color: #0000FF;">=</span><span style="color: #000000;">50</span> <span style="color: #008080;">then</span>
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"First 50 Blum integers:\n%s\n"</span><span style="color: #0000FF;">,{</span><span style="color: #7060A8;">join_by</span><span style="color: #0000FF;">(</span><span style="color: #000000;">Blum50</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">10</span><span style="color: #0000FF;">,</span><span style="color: #008000;">" "</span><span style="color: #0000FF;">,</span><span style="color: #000000;">fmt</span><span style="color: #0000FF;">:=</span><span style="color: #008000;">"%3d"</span><span style="color: #0000FF;">)})</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">count</span><span style="color: #0000FF;">=</span><span style="color: #000000;">26828</span> <span style="color: #008080;">or</span> <span style="color: #7060A8;">remainder</span><span style="color: #0000FF;">(</span><span style="color: #000000;">count</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1e5</span><span style="color: #0000FF;">)=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"The %,7d%s Blum integer is: %,9d\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">count</span><span style="color: #0000FF;">,</span><span style="color: #7060A8;">ord</span><span style="color: #0000FF;">(</span><span style="color: #000000;">count</span><span style="color: #0000FF;">),</span><span style="color: #000000;">n</span><span style="color: #0000FF;">})</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">count</span><span style="color: #0000FF;">=</span><span style="color: #000000;">4e5</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"\nPercentage distribution of the first 400,000 Blum integers:\n"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">,</span><span style="color: #000000;">n</span> <span style="color: #008080;">in</span> <span style="color: #000000;">counts</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">n</span> <span style="color: #008080;">then</span>
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">" %6.3f%% end in %d\n"</span><span style="color: #0000FF;">,</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">n</span><span style="color: #0000FF;">/</span><span style="color: #000000;">4000</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">})</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<!--

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''' python example for task rosettacode.org/wiki/Blum_integer '''
from sympy import factorint
def generate_blum():
''' Generate the Blum integers in series '''
for candidate in range(1, 10_000_000_000):
fexp = factorint(candidate).items()
if len(fexp) == 2 and sum(p[1] == 1 and p[0] % 4 == 3 for p in fexp) == 2:
yield candidate
print('First 50 Blum integers:')
lastdigitsums = [0, 0, 0, 0]
for idx, blum in enumerate(generate_blum()):
if idx < 50:
print(f'{blum: 4}', end='\n' if (idx + 1) % 10 == 0 else '')
elif idx + 1 in [26_828, 100_000, 200_000, 300_000, 400_000]:
print(f'\nThe {idx+1:,}th Blum number is {blum:,}.')
j = blum % 10
lastdigitsums[0] += j == 1
lastdigitsums[1] += j == 3
lastdigitsums[2] += j == 7
lastdigitsums[3] += j == 9
if idx + 1 == 400_000:
print('\n% distribution of the first 400,000 Blum integers is:')
for k, dig in enumerate([1, 3, 7, 9]):
print(f'{lastdigitsums[k]/4000:>8.5}% end in {dig}')
break

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use List::Divvy;
use Lingua::EN::Numbers;
sub is-blum(Int $n ) {
return False if $n.is-prime;
my $factor = find-factor($n);
return True if ($factor.is-prime && ( my $div = $n div $factor ).is-prime && ($div != $factor)
&& ($factor % 4 == 3) && ($div % 4 == 3));
False;
}
sub find-factor ( Int $n, $constant = 1 ) {
my $x = 2;
my $rho = 1;
my $factor = 1;
while $factor == 1 {
$rho *= 2;
my $fixed = $x;
for ^$rho {
$x = ( $x * $x + $constant ) % $n;
$factor = ( $x - $fixed ) gcd $n;
last if 1 < $factor;
}
}
$factor = find-factor( $n, $constant + 1 ) if $n == $factor;
$factor;
}
my @blum = lazy (2..Inf).hyper(:1000batch).grep: &is-blum;
say "The first fifty Blum integers:\n" ~
@blum[^50].batch(10)».fmt("%3d").join: "\n";
say '';
printf "The %9s Blum integer: %9s\n", .&ordinal-digit(:c), comma @blum[$_-1] for 26828, 1e5, 2e5, 3e5, 4e5;
say "\nBreakdown by last digit:";
printf "%d => %%%7.4f:\n", .key, +.value / 4e3 for sort @blum[^4e5].categorize: {.substr(*-1)}

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import "./math" for Int
import "./fmt" for Fmt
var inc = [4, 2, 4, 2, 4, 6, 2, 6]
// Assumes n is odd.
var firstPrimeFactor = Fn.new { |n|
if (n == 1) return 1
if (n%3 == 0) return 3
if (n%5 == 0) return 5
var k = 7
var i = 0
while (k * k <= n) {
if (n%k == 0) {
return k
} else {
k = k + inc[i]
i = (i + 1) % 8
}
}
return n
}
var blum = List.filled(50, 0)
var bc = 0
var counts = { 1: 0, 3: 0, 7: 0, 9: 0 }
var i = 1
while (true) {
var p = firstPrimeFactor.call(i)
if (p % 4 == 3) {
var q = i / p
if (q != p && q % 4 == 3 && Int.isPrime(q)) {
if (bc < 50) blum[bc] = i
counts[i % 10] = counts[i % 10] + 1
bc = bc + 1
if (bc == 50) {
System.print("First 50 Blum integers:")
Fmt.tprint("$3d ", blum, 10)
System.print()
} else if (bc == 26828 || bc % 1e5 == 0) {
Fmt.print("The $,9r Blum integer is: $,9d", bc, i)
if (bc == 400000) {
System.print("\n\% distribution of the first 400,000 Blum integers:")
for (i in [1, 3, 7, 9]) {
Fmt.print(" $6.3f\% end in $d", counts[i]/4000, i)
}
return
}
}
}
}
i = (i % 5 == 3) ? i + 4 : i + 2
}

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int Prime1;
func Semiprime(N); \Return 'true' if N is semiprime
int N, F, C;
[C:= 0; F:= 2;
repeat if rem(N/F) = 0 then
[C:= C+1;
Prime1:= N;
N:= N/F;
]
else F:= F+1;
until F > N;
return C = 2;
];
int N, C, Prime2;
[Format(4,0);
N:= 3; C:= 0;
loop [if Semiprime(N) then
[if rem(Prime1/4) = 3 then
[Prime2:= N/Prime1;
if Prime2 # Prime1 and rem(Prime2/4) = 3 then
[C:= C+1;
if C <= 50 then
[RlOut(0, float(N));
if rem(C/10) = 0 then CrLf(0);
];
if rem(C/1000)=0 then ChOut(0, ^.);
if C >= 26828 then
[Text(0, "^m^jThe 26828th Blum integer is: ");
IntOut(0, N); CrLf(0);
quit;
];
];
];
];
N:= N+2;
];
]

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include xpllib; \for Print
int Prime1;
func Semiprime(N); \Returns 'true' if odd N >= 3 is semiprime
int N, D, C;
[C:= 0; D:= 3;
while D*D <= N do
[while rem(N/D) = 0 do
[if C = 2 then return false;
C:= C+1;
N:= N/D;
];
D:= D+2;
];
Prime1:= N;
return C = 1;
];
int N, C, I, Goal, Prime2;
int FD, DC(10); \final digit and digit counters
[Text(0, "First 50 Blum integers:^m^j");
N:= 3; C:= 0; Goal:= 100_000;
for I:= 0 to 9 do DC(I):= 0;
loop [if Semiprime(N) then
[if rem(Prime1/4) = 3 then
[Prime2:= N/Prime1;
if rem(Prime2/4) = 3 and Prime2 # Prime1 then
[C:= C+1;
if C <= 50 then
[Print("%5d", N);
if rem(C/10) = 0 then Print("\n");
];
if C = 26_828 then
Print("\nThe 26,828th Blum integer is: %7,d\n", N);
if C = Goal then
[Print("The %6,dth Blum integer is: %7,d\n", Goal, N);
if Goal = 400_000 then quit;
Goal:= Goal + 100_000;
];
FD:= rem(N/10);
DC(FD):= DC(FD)+1;
];
];
];
N:= N+2;
];
Print("\n% distribution of the first 400,000 Blum integers:\n");
for I:= 0 to 9 do
if DC(I) > 0 then
Print("%4.3f\% end in %d\n", float(DC(I)) / 4_000., I);
]