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A034185
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Number of symmetric n X 3 crossword puzzle grids.
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3
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1, 3, 11, 21, 61, 111, 309, 565, 1563, 2859, 7907, 14459, 39991, 73117, 202227, 369729, 1022587, 1869581, 5170829, 9453757, 26146909, 47804041, 132214959, 241726811, 668560673, 1222320359, 3380656559, 6180808253, 17094691953, 31253992007, 86441342981
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OFFSET
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1,2
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COMMENTS
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Rules: all white squares are edge connected; at least 1 white square on every edge of grid; symmetric ones have 180-degree rotational symmetry.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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