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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. 3
1, 2, 20, 269, 8116, 519400, 67566361, 17518353991, 9334778743018, 10240638005472594, 23244895727823155064 (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 both left-right and top-bottom mirror symmetry, and the set of white squares must be connected.

LINKS

Table of n, a(n) for n=1..11.

CROSSREFS

Cf. A323838, A323839, A325408.

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

Sequence in context: A207151 A272568 A229727 * A155671 A303616 A231499

Adjacent sequences:  A325406 A325407 A325408 * A325410 A325411 A325412

KEYWORD

nonn,more

AUTHOR

Michael Kleber, Apr 23 2019

EXTENSIONS

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

STATUS

approved

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Last modified May 31 22:20 EDT 2020. Contains 334756 sequences. (Running on oeis4.)