ref: faa625a1d5ab47ac0438b2cea5b2bde1ea747b8b
dir: /sys/games/lib/sudoku/boards/hard-2005-04-23.su/
.3..47.8. .261..7.. 4.......6 3..42.... .4.7.3.5. ....98..3 5.......8 ..8..437. .7.86..9. 931647285 826135749 457289136 385426917 649713852 712598463 594371628 268954371 173862594