ref: a30f99a4e64b55d80e9bd0d4485972a20bfa2a95
dir: /sys/games/lib/sudoku/boards/medium-2005-04-21.su/
...9..3.. 3.9.....1 ...15...4 8....642. .3..4..7. .743....9 6...81... 9.....2.8 ..2..4... 415967382 369428751 728153694 891576423 236849175 574312869 653281947 947635218 182794536