A323838 Number of (2n+1) X (2n+1) black-and-white grids that are legal for crossword puzzles.

1, 15, 397, 35324, 18446134, 41752489852, 409764131469787, 17368974525101032256, 3195393813996265512672344, 2544868518166378264304163732974

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. A323839, 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