ref: a07a2025dab770421992362d8f4e4acbbf776fa8
dir: /sys/games/lib/sudoku/boards/hard-2005-05-14.su/
..5..6... 26..95.7. ..9...... 91...7.8. ..39.81.. .7.1...39 ......7.. .3.64..98 ...5..2.. 345786912 261395874 789421356 916237485 453968127 872154639 524819763 137642598 698573241