$ perl -Mstrict -Mwarnings -E '
my @nums  = qw{ 1 2 3 };
my @ltrs  = qw{ a b c };
my $iters = 2;

for my $iter ( 1 .. $iters )
{
    for my $num ( @nums )
    {
        for my $ltr ( @ltrs )
        {
            say qq{$num$ltr};
        }
    }
}'
1a
1b
1c
2a
2b
2c
3a
3b
3c
1a
1b
1c
2a
2b
2c
3a
3b
3c
$