A323839 Number of (2n+1) X (2n+1) black-and-white grids that are legal for crossword puzzles and have no all-black edges.

1, 12, 312, 31187, 17438702, 40575832476, 404139015237875, 17253201646564115439, 3185118492387669085270268, 2540927098290913247876202007100

Offset: 1

Author

N. J. A. Sloane, Feb 04 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 180-degree rotation, and the set of white squares must be connected.

Computed by Michael Kleber.

References

• Michael Kleber, Posting to Math Fun Mailing List, Feb 04 2019.

Crossrefs

Cf. A323838, A325408, A325409

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

Extensions

a(4)-a(7) corrected by Michael Kleber, Feb 06 2019

a(8)-a(10) added by Michael Kleber, Apr 23 2019