ref: e77fa31516bc5dc834f1caf1f4ed3d888a9aa810
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