回复：回复：现在最难的数独仅17字,但数学家还没有证明17是最小的.

Your list is interesting but kind of old. For example we have now known 106 horizontally symmetrical puzzles with 18 clues,for example

1 . . . . . . . 3
2 . . . . . . . 4
. . 7 8 . 4 6 . .
. . 6 . . . 9 . .
. . . . . . . . .
5 . . . 3 . . . 1
3 . . . . . . . 2
. . . . 1 . . . .
. . . 9 . 8 . . .