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%I #17 Apr 24 2019 06:04:37
%S 1,12,312,31187,17438702,40575832476,404139015237875,
%T 17253201646564115439,3185118492387669085270268,
%U 2540927098290913247876202007100
%N Number of (2n+1) X (2n+1) black-and-white 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 180-degree rotation, and the set of white squares must be connected.
%C Computed by _Michael Kleber_.
%D Michael Kleber, Posting to Math Fun Mailing List, Feb 04 2019.
%Y Cf. A323838, A325408, A325409
%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 _N. J. A. Sloane_, Feb 04 2019
%E a(4)-a(7) corrected by _Michael Kleber_, Feb 06 2019
%E a(8)-a(10) added by _Michael Kleber_, Apr 23 2019