From 3dd6776d41b9e689f49f64a96dcf688ab91ea21e Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Sun, 23 Jul 2017 21:45:25 -0400
Subject: problem 357

---
 357.pl | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100755 357.pl

(limited to '357.pl')

diff --git a/357.pl b/357.pl
new file mode 100755
index 0000000..dd20ab6
--- /dev/null
+++ b/357.pl
@@ -0,0 +1,32 @@
+#!/usr/bin/perl
+use strict;
+use warnings;
+use 5.014;
+use List::Util qw/all/;
+use Math::Prime::XS qw/sieve_primes/;
+use Math::Factor::XS qw/factors/;
+
+say "calculating primes...";
+my @primes = sieve_primes(1e8);
+my %primes = map { $_, 1 } @primes;
+say "done (found " . @primes . " primes)";
+
+my $total = 0;
+
+# handle 2 separately (1 + 1/1 = 2, which is prime)
+shift @primes;
+$total += 1;
+
+for my $i (@primes) {
+    my $n = $i - 1;
+    # because here we assume odd primes
+    next unless $primes{2 + $n / 2};
+
+    my @factors = factors($n);
+    @factors = @factors[0..(@factors / 2)] if @factors > 0;
+    if (all { $primes{$_ + $n / $_} } @factors) {
+        $total += $n;
+    }
+}
+
+say $total;
-- 
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