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#!/bin/env perl
use Modern::Perl;
use integer;
my $i = 0;
my %sods;
my $cnt = 0;
while (1) {
$sods{ $i } = sod($i) unless defined $sods{ $i };
my $v = $sods{ $i };
if ($v > $i) {
$sods{ $v } = sod($v) unless defined $sods{ $v };
if ($i == $sods{ $v }) {
say "$i $v";
last if ++$cnt == 5;
}
}
++$i;
}
# sum of proper divisors
sub sod {
my $n = shift;
my $sum = 0;
my @a = (1) x ($n/2 + 1);
for (my $i = 1; $i < $n/2 + 1; ++$i) {
next unless $a[$i];
if ($n % $i) {
my $j = $i;
while ($j <= $n/2 + 1) {
$a[$j] = 0;
$j += $i;
}
} else {
$sum += $i;
}
}
return $sum;
}
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