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A323838
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Number of (2n+1) X (2n+1) black-and-white grids that are legal for crossword puzzles.
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3
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OFFSET
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1,2
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COMMENTS
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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.
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REFERENCES
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Michael Kleber, Posting to Math Fun Mailing List, Feb 04 2019.
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LINKS
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Table of n, a(n) for n=1..10.
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CROSSREFS
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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
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KEYWORD
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nonn,more
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AUTHOR
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N. J. A. Sloane, Feb 04 2019
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EXTENSIONS
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a(4)-a(7) corrected by Michael Kleber, Feb 06 2019
a(8)-a(10) added by Michael Kleber, Apr 23 2019
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STATUS
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approved
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