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A211035
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1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor
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0
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1, 4, 40, 800, 33432, 2888696, 517902680, 192533704008, 148429379845856, 237284500891487840, 786611979025079107456, 5407447771030956200932952, 77084070831919712319047890192, 2278648745820732735808198902023640
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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
..1..0..2..2....2..1..0..0....0..1..0..2....0..1..1..0....1..2..1..0
..0..1..0..0....1..0..2..1....1..2..0..2....1..2..0..2....2..0..1..2
..2..0..1..2....0..2..0..2....0..0..2..0....1..0..2..0....1..1..0..1
..2..0..2..1....0..1..2..0....2..2..0..1....0..2..0..1....0..2..1..0
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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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