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A211046
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or two horizontal and vertical neighbors
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0
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1, 5, 40, 516, 10632, 351016, 18493208, 1556661888, 208981813872, 44758689895632, 15281461874812576, 8316915639373762736, 7212900527703818038976
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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
..0..0..2..0....2..0..1..2....2..1..2..0....0..1..0..1....2..1..0..1
..0..0..1..1....0..2..2..1....1..0..0..1....1..0..1..2....1..2..1..0
..2..1..1..1....1..2..2..0....2..0..0..2....0..1..0..0....0..1..0..2
..0..1..1..0....2..1..0..1....0..1..2..0....1..2..0..0....1..0..2..1
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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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