Data commit

Task/Untouchable-numbers/Raku/untouchable-numbers.raku

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+# 20210220 Raku programming solution
+
+sub propdiv (\x) {
+   my @l = 1 if x > 1;
+   (2 .. x.sqrt.floor).map: -> \d {
+      unless x % d { @l.push: d; my \y = x div d; @l.push: y if y != d }
+   }
+   @l
+}
+
+sub sieve (\n) {
+   my %s;
+   for (0..(n+1)) -> \k {
+      given ( [+] propdiv k ) { %s{$_} = True if $_ ≤ (n+1) }
+   }
+   %s;
+}
+
+my \limit = 1e5;
+my %c = ( grep { !.is-prime }, 1..limit ).Set; # store composites
+my %s = sieve(14 * limit);
+my @untouchable = 2, 5;
+
+loop ( my \n = $ = 6 ; n ≤ limit ; n += 2 ) {
+   @untouchable.append(n) if (!%s{n} && %c{n-1} && %c{n-3})
+}
+
+my ($c, $last) = 0, False;
+for @untouchable.rotor(10) {
+   say [~] @_».&{$c++ ; $_ > 2000 ?? ( $last = True and last ) !! .fmt: "%6d "}
+   $c-- and last if $last
+}
+
+say "\nList of untouchable numbers ≤ 2,000 : $c \n";
+
+my ($p, $count) = 10,0;
+BREAK: for @untouchable -> \n {
+   $count++;
+   if (n > $p) {
+      printf "%6d untouchable numbers were found  ≤ %7d\n", $count-1, $p;
+      last BREAK if limit == ($p *= 10)
+   }
+}
+printf "%6d untouchable numbers were found  ≤ %7d\n", +@untouchable, limit