ref: dd820435e922d927c4f1531fb82aec2bf8fc5cd3
dir: /sys/games/lib/sudoku/boards/medium-2005-02-19.su/
5....921. 8.7.52... .3...1... ..4....8. .53.1.94. .8....6.. ...4...3. ...16.8.2 .219....6 546739218 817652394 932841765 274396581 653218947 189574623 768425139 495163872 321987456