Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #12 Jun 22 2019 00:45:35
%S 1,5,35,436,11348,650798,78816939,19500572516,10050221059942,
%T 10777659213636406,24081651896803403442
%N Number of (2n+1) X (2n+1) black-and-white mirror-symmetric grids that are legal for crossword puzzles.
%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, 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 _Michael Kleber_, Apr 23 2019
%E a(11) added by _Akshay Ravikumar_, Jun 20 2019