ref: b51b623725ce394a1f9f12686f043c1cc3bba7c9
dir: /sys/games/lib/sudoku/boards/hard-2005-05-15.su/
7...1...6 ..25.4... ..4.9.... 2....58.3 .5.2.6.7. 1.79....2 ....8.3.. ...3.19.. 4...2...8 735812496 982564731 614793285 269175843 358246179 147938652 521489367 876351924 493627518