ref: 06335925f66a7b4da09c849c21e96eb43e1c9be9
dir: /sys/games/lib/sudoku/boards/medium-2005-05-18.su/
....4.... 57.1.6..2 .2..9.78. .5....8.. .6.7.9.5. ..9....1. .42.6..3. 6..3.4.28 ....7.... 981247365 573186942 426593781 254631879 168729453 739458216 842965137 697314528 315872694