ref: fdf020f1309bffde33554f5a13c7b3a1a3fb1891
dir: /sys/games/lib/sudoku/boards/medium-2005-01-28.su/
...5.9..3 ....6..4. 2...43..8 189.....4 ..4...3.. 3.....785 5..67...1 .7..1.... 9..4.2... 647589123 835261947 291743658 189357264 754826319 362194785 523678491 476915832 918432576