#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

my $seq = 'AAGAATGCCAGTTTGTAAGTACTGACTTTGGAAAA';

my $x = 'A';
my $c = () = $seq =~ /$x/g;  # $c is now 13
my $mod = 2;
my ($quot, $rem) = (int $c / $mod, $c % $mod);

say "Number of occurences: " . $c;
say "Number of pairs: " . $quot;
say "Remainder: " . $rem;

__END__

$ perl test.pl
Number of occurences: 13
Number of pairs: 6
Remainder: 1