ref: f341ae8c777dda2876beb4d4a1c67c4e920595ca
dir: /sys/games/lib/sudoku/boards/medium-2005-04-29.su/
5.1....7. ..94....2 .6..1.9.8 ...1..784 ......... 254..6... 4.5.7..3. 1....24.. .9....1.5 541298673 879463512 362517948 936125784 718349256 254786391 425671839 183952467 697834125