A325409 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.

1, 2, 20, 269, 8116, 519400, 67566361, 17518353991, 9334778743018, 10240638005472594, 23244895727823155064

Offset: 1

Author

Michael Kleber, Apr 23 2019

Keywords

• nonn
• more

Comments

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.

Crossrefs

Cf. A323838, A323839, A325408.

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

Extensions

a(11) added by Akshay Ravikumar, Jun 20 2019