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A211040
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors
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0
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1, 4, 40, 928, 45128, 4945168, 1207742160, 655725571768, 791701825710768, 2127149017683661104, 12717092443922120808584, 169157473880575759274475472, 5006302388939519643670779061032
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OFFSET
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1,2
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LINKS
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EXAMPLE
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Some solutions for n=4
..2..1..2..2....0..1..0..2....1..0..0..1....2..0..2..1....1..0..1..0
..1..0..1..1....1..2..0..1....0..1..2..1....0..1..0..0....0..2..0..2
..2..1..0..2....0..0..2..1....0..2..0..2....2..0..2..1....1..0..2..1
..2..1..2..0....2..1..1..2....1..1..2..0....1..0..1..0....0..2..1..2
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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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