perl/p3.pl


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#!/usr/bin/env perl

use strict;
use warnings;

use List::Util qw(all);

my $n = 600851475143;

# Functional

# Imperative
my @primes;
my $last_factor;

for my $i (2 .. $n) {
	last if ($i > $n);
	if (all { $i % $_ != 0 } @primes) {
		if ($n % $i == 0) {
			$n /= $i;
			$last_factor = $i;
			redo;
		}
		push(@primes, $i);
	}
}
print "$last_factor\n";