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Number of (2n+1) X (2n+1) black-and-white mirror-symmetric grids that are legal for crossword puzzles and have no all-black edges.
3

%I #11 Jun 22 2019 00:45:43

%S 1,2,20,269,8116,519400,67566361,17518353991,9334778743018,

%T 10240638005472594,23244895727823155064

%N Number of (2n+1) X (2n+1) black-and-white mirror-symmetric grids that are legal for crossword puzzles and have no all-black edges.

%C Rules: Every white square must be "checked" (in both a horizontal and vertical word), words must be at least 3 letters long, the whole grid must be symmetric under both left-right and top-bottom mirror symmetry, and the set of white squares must be connected.

%Y Cf. A323838, A323839, A325408.

%Y There are many other OEIS sequences related to crossword puzzles: search for "crossword puzzle" (without the quotes).

%K nonn,more

%O 1,2

%A _Michael Kleber_, Apr 23 2019

%E a(11) added by _Akshay Ravikumar_, Jun 20 2019