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A325409
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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.
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3
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1, 2, 20, 269, 8116, 519400, 67566361, 17518353991, 9334778743018, 10240638005472594, 23244895727823155064
(list;
graph;
refs;
listen;
history;
text;
internal format)
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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 both left-right and top-bottom mirror symmetry, and the set of white squares must be connected.
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LINKS
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Table of n, a(n) for n=1..11.
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CROSSREFS
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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
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KEYWORD
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nonn,more
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AUTHOR
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Michael Kleber, Apr 23 2019
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EXTENSIONS
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a(11) added by Akshay Ravikumar, Jun 20 2019
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STATUS
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approved
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