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A211047
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to one or two horizontal and vertical neighbors
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0
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0, 1, 4, 102, 3452, 306196, 56305300, 23135879808, 20936361314520, 41767961477927304, 184066448459881652770, 1789009177710334924490408
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OFFSET
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1,3
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LINKS
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EXAMPLE
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Some solutions for n=4
..1..1..2..2....2..2..1..2....2..2..1..1....0..0..2..2....0..0..1..2
..1..1..2..2....2..2..1..2....2..2..2..1....0..1..1..1....0..1..1..2
..2..2..1..1....1..1..1..0....1..2..2..2....2..1..2..2....1..1..0..0
..2..2..1..1....2..2..0..0....1..1..2..2....2..1..2..2....2..2..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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