Data commit

Task/Duffinian-numbers/Perl/duffinian-numbers.pl

@@ -0,0 +1,26 @@
+use strict;
+use warnings;
+use feature <say state>;
+use List::Util 'max';
+use ntheory qw<divisor_sum is_prime gcd>;
+
+sub table { my $t = shift() * (my $c = 1 + max map {length} @_); ( sprintf( ('%'.$c.'s')x@_, @_) ) =~ s/.{1,$t}\K/\n/gr }
+
+sub duffinian {
+    my($n) = @_;
+    state $c = 1; state @D;
+    do { push @D, $c if ! is_prime ++$c and 1 == gcd($c,divisor_sum($c)) } until @D > $n;
+    $D[$n];
+}
+
+say "First 50 Duffinian numbers:";
+say table 10, map { duffinian $_-1 } 1..50;
+
+my(@d3,@triples) = (4, 8, 9); my $n = 3;
+while (@triples < 39) {
+    push @triples, '('.join(', ',@d3).')' if $d3[1] == 1+$d3[0] and $d3[2] == 2+$d3[0];
+    shift @d3 and push @d3, duffinian ++$n;
+}
+
+say 'First 39 Duffinian triplets:';
+say table 3, @triples;