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#!/usr/bin/env perl
use strict;
use warnings;
use experimental qw{ say postderef signatures state };
use List::Util qw{ product uniq };
$| = 1;
map { primorial($_) } 0 .. 9;
sub primorial ( $n ) {
my @primes = primes($n);
my $primes = join 'x', @primes;
my $p = product @primes;
say <<"END";
P($n) = $p ($primes)
END
}
sub primes ( $i ) {
state $primes;
$primes->[0] = 1;
if ( !defined $primes->[$i] ) {
my $iter = make_iterator( $primes->[-1] );
while ( my $p = $iter->() ) {
next unless is_prime($p);
push $primes->@*, $p;
$primes->@* = uniq $primes->@*;
last if defined $primes->[$i];
}
}
return $primes->@[ 0 .. $i ];
}
sub is_prime ($n) {
die "Bad number $n" unless length $n;
return 0 if $n == 0;
return 0 if $n == 1;
for ( 2 .. sqrt $n ) { return 0 unless $n % $_ }
return 1;
}
sub make_iterator($n) {
return sub {
state $v = $n;
return $v++;
}
}
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