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A211051
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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, 45, 801, 27967, 1940165, 265677267, 71849269093, 38284388785363, 40154074645523977, 82859490626738386321, 336329579954192837096611, 2685093328682215861465741329
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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
..0..1..0..0....0..1..0..1....2..0..2..0....2..2..2..2....2..1..2..2
..1..0..0..0....1..2..1..2....0..1..0..1....2..0..1..2....1..2..2..2
..0..0..2..1....0..1..2..0....2..0..1..0....2..1..2..2....2..2..2..2
..0..0..1..2....1..2..0..1....0..1..0..2....2..2..2..0....2..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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