my @test = qw(A B Z AA AC BA ABC);

sub SIZE_ALPHABET() { scalar (() = 'A'..'Z') }

for my $test (@test) {
        my $num = 0;
        for my $idx (0..length($test) -1) {
                my $char = substr($test, -$idx-1, 1);
                $num += ((ord($char) - ord('A') + 1) * (SIZE_ALPHABET ** $idx));
        }
        
        say "$test = $num";
}