ref: d7613e356c55a3b7a1140a1f6d8aa6dca43b9d97
dir: /sys/games/lib/sudoku/boards/medium-2005-04-21.su/
...9..3.. 3.9.....1 ...15...4 8....642. .3..4..7. .743....9 6...81... 9.....2.8 ..2..4... 415967382 369428751 728153694 891576423 236849175 574312869 653281947 947635218 182794536