ref: 1f8e6c916af4d10928b751c3bd8c3a6355267c39
dir: /sys/games/lib/sudoku/boards/medium-2005-04-15.su/
1.9..7... .36..8... ..7..1.28 ...81...6 ..5...7.. 9...45... 42.1..5.. ...5..61. ...2..9.4 189327465 236458197 547961328 374819256 815632749 962745831 428196573 793584612 651273984