%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