probably has something to do with it being Japanese….

The Independent ( A UK Newspaper ) has released a version in its weekend edition of a 4 x 4 grid (256 squares), called the Super Soduko.

Because we run out of numbers at 9, it uses the computer number base hexadecimal, which uses the letters a - f to signify 11 - 16.

So you actually needs to use the symbols 0 thru 9 and A, B, C, D, E and F….yikes!