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A211092
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1/4 the number of n X n 0..3 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, 1, 19, 136, 3496, 100204, 6012109, 537556135, 86449986124, 22576823498161, 10130717811503530, 7577956550025798379
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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
..3..3..2..2....0..0..2..2....3..3..0..0....2..2..2..2....3..3..1..1
..3..3..2..2....0..0..2..2....3..3..0..0....2..2..2..2....3..3..1..1
..2..2..2..2....2..2..3..3....0..0..0..0....2..2..3..3....1..1..1..1
..2..2..2..2....2..2..3..3....0..0..0..0....2..2..3..3....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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