ref: aad36c645ab7b9ab376a935ca7aa63b7d303c46f
dir: /sys/games/lib/sudoku/boards/medium-2005-02-23.su/
...61..7. .....4.2. 7.352..8. .39..6... ..4.5.3.. ...1..54. .2..816.4 .6.3..... .4..67... 452618973 698734125 713529486 539476218 174852369 286193547 327981654 861345792 945267831