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A211090
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1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.
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1
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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..0..0..0....0..0..1..3....0..2..2..2....2..2..2..2....0..2..2..3
..0..2..3..1....0..0..3..0....2..2..3..0....2..0..3..1....2..0..0..2
..0..3..3..1....1..3..2..1....2..3..2..3....2..3..2..1....2..0..0..1
..0..1..1..1....3..0..1..1....2..0..3..2....2..1..1..1....3..2..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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