ref: a696951c6cbad354373a820ed1d14e25697d1fa3
dir: /sys/games/lib/sudoku/boards/medium-2005-05-04.su/
...9.2..8 ....8.9.. .8.....75 .52.9...3 ....1.... 8...5.64. 92.....1. ..4.7.... 1..6.4... 715962438 243587961 689341275 452796183 367418592 891253647 926835714 534179826 178624359