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A211038
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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, 72, 2088, 148758, 21763840, 7132571384, 5048293367644, 7844581606488974, 26582841246234004080, 197025807090354544802766
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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
..0..0..2..2....0..0..2..2....2..2..1..1....0..0..0..0....2..2..2..2
..0..1..1..2....0..1..1..1....2..2..1..2....0..1..1..0....2..0..0..1
..2..1..0..0....2..1..0..0....1..1..1..2....0..1..2..2....2..0..0..1
..2..2..0..0....2..1..0..0....1..2..2..2....0..0..2..2....2..1..1..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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