ref: 1f8e6c916af4d10928b751c3bd8c3a6355267c39
dir: /sys/games/lib/sudoku/boards/hard-2005-04-03.su/
.2...6.7. ..62.5... 3..9....1 4...3.1.. 15.....34 ..8.5...9 9....3..6 ...8.94.. .8.1...9. 821346975 796215348 345987621 469738152 157692834 238451769 914573286 572869413 683124597