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A211052
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to one, two or three horizontal and vertical neighbors
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1
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0, 1, 9, 239, 14669, 2313041, 915560157, 915512113455, 2309733753013069, 14705975948890342013, 236286306641789616616527, 9580759647090339471565196845, 980341335177418943590433413869387
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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..1..0....1..1..2..2....1..1..0..0....2..2..0..2....0..0..1..1
..0..1..1..0....1..1..2..1....1..1..1..1....2..2..0..2....0..0..2..2
..1..1..1..1....2..2..1..1....0..1..1..0....0..0..2..2....1..2..2..2
..0..0..1..1....2..1..1..1....0..1..0..0....2..2..2..2....1..2..2..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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