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- #!/usr/bin/perl
- # Daniel "Trizen" Șuteu
- # License: GPLv3
- # Date: 12 May 2017
- # https://github.com/trizen
- # https://projecteuler.net/problem=130
- # Runtime: 2.814s
- use 5.010;
- use strict;
- use warnings;
- use ntheory qw(gcd powmod is_prime);
- my $sum = 0;
- my $count = 0;
- for (my $n = 2 ; ; ++$n) {
- is_prime($n) && next;
- gcd($n, 10) != 1 && next;
- my $r = 1;
- my $p = 0;
- foreach my $k (1 .. $n - 1) {
- $r += powmod(10, $k, $n);
- $r %= $n;
- $p += 1;
- last if ($r == 1);
- }
- if ($r == 1 and ($n - 1) % $p == 0) {
- $sum += $n;
- last if ++$count == 25;
- }
- }
- say $sum;
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