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A211037
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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, 34, 398, 6988, 197328, 8645790, 598407040, 64812874208, 11032788701886, 2945294560303704, 1234174982814619524, 811373195193470813704
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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
..1..1..1..0....2..1..1..1....1..0..2..0....2..1..0..1....1..1..0..2
..1..0..1..2....1..1..2..1....0..2..0..2....1..0..1..0....1..1..2..1
..1..1..1..0....1..2..0..1....2..0..2..0....0..1..2..1....0..2..1..2
..0..2..0..1....1..1..1..1....0..2..0..1....1..0..1..0....2..1..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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