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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=1..10.

CROSSREFS

Cf. A323839, A325408, A325409.

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

Sequence in context: A157581 A143001 A250950 * A278981 A279133 A034675

Adjacent sequences:  A323835 A323836 A323837 * A323839 A323840 A323841

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

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Last modified August 8 08:27 EDT 2020. Contains 336293 sequences. (Running on oeis4.)