ref: 1333b4d14e088d018a485e6b9b034449032267f4
dir: /sys/games/lib/sudoku/boards/medium000.su/
.2..3..9. ...9.7... 9..2.8..5 ..48.65.. 6.7...2.8 ..31.29.. 8..6.5..7 ...3.9... .3..2..5. 428531796 365947182 971268435 214896573 697453218 583172964 849615327 752389641 136724859