#!/usr/bin/env perl
use warnings;
use strict;
use Math::Prime::Util qw/:all/;
# Brute force using MPU's divisor_sum.
# MPU v0.38 1.5 minutes
# Pari 3.5 minutes:
# s=0; for(n=1,64000000-1,if(issquare(sigma(n,2)),s=s+n;))
my $n = shift || 64_000_000;
my $sum = 0;
foreach my $i (0 .. $n-1) {
$sum += $i if is_power( divisor_sum($i, 2) , 2);
}
print "$sum\n";