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- #!/usr/bin/perl
- # Author: Daniel "Trizen" Șuteu
- # License: GPLv3
- # Website: https://github.com/trizen
- # How many composite integers, n < 10^8, have precisely two, not necessarily distinct, prime factors?
- # https://projecteuler.net/problem=187
- # Runtime: 2.402s
- use 5.010;
- use strict;
- use warnings;
- use ntheory qw(primes);
- my $limit = 10**8;
- my $primes = primes(0, $limit / 2);
- my $count = 0;
- my $end = $#{$primes};
- foreach my $i (0 .. $end) {
- foreach my $j ($i .. $end) {
- $primes->[$i] * $primes->[$j] >= $limit ? last : ++$count;
- }
- }
- say $count;
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