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A211045
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors
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0
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1, 4, 48, 1104, 54408, 5624336, 1223018480, 559805180336, 539124008193384, 1092375543732930912, 4656812532055124194440, 41767144321757757477117792
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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....1..0..2..0....1..2..1..2....1..0..1..2....2..0..2..1
..1..0..1..0....0..2..1..2....2..0..1..0....0..2..0..0....0..2..0..1
..2..1..0..1....2..1..1..1....1..1..2..0....1..0..2..1....2..0..1..0
..2..0..1..2....0..2..1..2....2..0..0..2....2..0..1..2....1..1..0..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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