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A211041
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to two or three horizontal and vertical neighbors.
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0
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0, 1, 0, 6, 8, 118, 880, 14400, 318220, 10446298, 531060152, 39577654480, 4465022457276, 757302604610482, 191605833481050984
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OFFSET
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1,4
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LINKS
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EXAMPLE
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Some solutions for n=4
..0..0..1..1....0..0..1..1....2..2..0..0....2..2..1..1....1..1..1..1
..0..0..1..1....0..0..1..1....2..2..0..0....2..2..1..1....1..2..2..1
..1..1..0..0....1..1..2..2....0..0..1..1....1..1..2..2....1..2..2..1
..1..1..0..0....1..1..2..2....0..0..1..1....1..1..2..2....1..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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