Data commit

Task/Additive-primes/ALGOL-W/additive-primes.alg

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+begin % find some additive primes - primes whose digit sum is also prime %
+    % sets p( 1 :: n ) to a sieve of primes up to n %
+    procedure Eratosthenes ( logical array p( * ) ; integer value n ) ;
+    begin
+        p( 1 ) := false; p( 2 ) := true;
+        for i := 3 step 2 until n do p( i ) := true;
+        for i := 4 step 2 until n do p( i ) := false;
+        for i := 3 step 2 until truncate( sqrt( n ) ) do begin
+            integer ii; ii := i + i;
+            if p( i ) then for pr := i * i step ii until n do p( pr ) := false
+        end for_i ;
+    end Eratosthenes ;
+    integer MAX_NUMBER;
+    MAX_NUMBER := 500;
+    begin
+        logical array prime( 1 :: MAX_NUMBER );
+        integer       aCount;
+        % sieve the primes to MAX_NUMBER %
+        Eratosthenes( prime, MAX_NUMBER );
+        % find the primes that are additive primes %
+        aCount := 0;
+        for i := 1 until MAX_NUMBER - 1 do begin
+            if prime( i ) then begin
+                integer dSum, v;
+                v    := i;
+                dSum := 0;
+                while v > 0 do begin
+                    dSum := dSum + v rem 10;
+                    v    := v div 10
+                end while_v_gt_0 ;
+                if prime( dSum ) then begin
+                    writeon( i_w := 4, s_w := 0, " ", i );
+                    aCount := aCount + 1;
+                    if aCount rem 20 = 0 then write()
+                end if_prime_dSum
+            end if_prime_i
+        end for_i ;
+        write( i_w := 1, s_w := 0, "Found ", aCount, " additive primes below ", MAX_NUMBER )
+    end
+end.