ref: 1e9bb75854a336de2a63f9a4fb4d67dd75d682f1
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