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A323838
Number of (2n+1) X (2n+1) black-and-white grids that are legal for crossword puzzles.
3
1, 15, 397, 35324, 18446134, 41752489852, 409764131469787, 17368974525101032256, 3195393813996265512672344, 2544868518166378264304163732974
OFFSET
1,2
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
There are many other OEIS sequences related to crossword puzzles: search for "crossword puzzle" (without the quotes).
Sequence in context: A373872 A250950 A366300 * A278981 A279133 A034675
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Feb 04 2019
EXTENSIONS
a(4)-a(7) corrected by Michael Kleber, Feb 06 2019
a(8)-a(10) added by Michael Kleber, Apr 23 2019
STATUS
approved