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A191508
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Number of n X n symmetric binary matrices with each 1 adjacent to no more than 3 horizontally or vertically neighboring 1's.
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1
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2, 8, 56, 792, 21984, 1188160, 125522112, 25932064896, 10472077118464, 8266074697979136, 12754433913314441216, 38469498012053658897408, 226810241439860068417249280, 2613967215944945112514234085376
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OFFSET
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1,1
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LINKS
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EXAMPLE
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Some solutions for n=4
..0..1..0..0....0..0..1..1....0..0..0..1....0..0..0..1....1..0..0..0
..1..0..1..0....0..0..0..1....0..0..0..1....0..1..1..1....0..0..1..0
..0..1..0..1....1..0..0..0....0..0..0..1....0..1..1..0....0..1..0..0
..0..0..1..1....1..1..0..1....1..1..1..0....1..1..0..1....0..0..0..0
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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