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A211042
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, two or three horizontal and vertical neighbors
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0
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1, 5, 34, 504, 12656, 595218, 51772998, 8410205156, 2530816613400, 1415636007880172, 1467795266440304666, 2820089447984802286032
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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..0..1..0....2..2..2..1....2..0..2..0....2..1..0..0....0..1..2..0
..0..2..0..2....2..0..2..2....0..2..0..2....1..2..0..0....1..2..0..2
..1..0..1..1....2..2..0..2....2..0..2..1....0..0..0..1....2..0..1..0
..0..2..1..1....1..2..2..2....0..2..1..2....0..0..1..0....0..2..0..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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