ref: 38c2cdf164f0cc12db65f9f51b3b4a7815543d12
dir: /sys/games/lib/sudoku/boards/medium-2005-04-20.su/
....5.21. .2.7..6.9 ..7..6... ..1...54. 58..2..96 .93...1.. ...1..4.. 7.5..4.6. .39.6.... 346958217 128743659 957216384 271689543 584321796 693475128 862197435 715834962 439562871