The bottom part has 5 digits, but the top part only has 4 (counting blank as digit 0). If both had 5 digits there would have been 5×5=25 positional digits. So

The bottom part has 5 digits, but the top part only has 4 (counting blank as digit 0). If both had 5 digits there would have been 5×5=25 positional digits. So it’s kind of base 5, base 4, and base 20 at the same time.