ref: c247ce1c3301222ccd445d3479c29f7eb0e9bfc4
dir: /sys/games/lib/sudoku/boards/hard-2005-04-02.su/
.....96.. ...15.... 58..37..4 3......8. 1.6...4.7 .2......6 7..86..91 ....23... ..37..... 237489615 469152873 581637924 374516289 156298437 928374156 742865391 615923748 893741562