ref: ec7a543450ad5c0ed2eeb32f45a1e57a36c47ac7
dir: /sys/games/lib/sudoku/boards/medium-2005-04-01.su/
...74.8.. ....137.9 ..1...65. 4..9..... 31.....68 .....4..5 .54...2.. 6.735.... ..8.92... 593746812 286513749 741829653 465938127 319275468 872164395 954687231 627351984 138492576