ref: fbf9f131b5931defb02ff08d54d1e088d9f51a15
dir: /sys/games/lib/sudoku/boards/hard-2005-03-13.su/
...4..2.7 ...1.3.4. 6.....5.1 ..82.71.6 ......... 2.53.97.. 8.4.....2 .2.7.4... 7.3..5... 381456297 592173648 647982531 938247156 476518923 215369784 854691372 129734865 763825419