Normal 6x6 Sudoku rules apply.
The 6x6 boxes are numbered as usual. Some box numbers are helpfully indicated by the given digits.
In boxes 1 to 4, two orthogonally adjacent digits in the same box must not have the box number as their difference.
In boxes 5 and 6, two orthogonally adjacent digits in the same box must not have the box number as their sum.
In every box, the digit that corresponds to the box number (e.g. the 1 in box 1) must sit adjacent to a 5 or 6 in the same box (it may, but doesn't have to, sit adjacent to both).
Solution code: Column 5 (second from the right), top to bottom
on 29. January 2026, 07:46 by balpha
German translation added
on 28. January 2026, 22:21 by dzamie
Pretty neat! The changing of the rule for boxes 5+6 makes sense, but did give me a bit of pause.
[balpha:] Thanks! Yeah, initially I tried it so that in all six boxes neither difference nore sum could match, but it turns that there is no solution for that. So I had to compromise.
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