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A210921
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Number of n X n 0..3 symmetric matrices with every element equal to zero or two horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order.
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0
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1, 3, 39, 2107, 277902, 87883641, 66460660741, 120226326939778, 520179215730042235, 5383068220104980704743, 133236771262960489496028245
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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..3....0..0..1..1....0..1..1..1....0..1..0..1....0..1..2..3
..1..2..1..2....0..0..1..1....1..1..0..1....1..0..1..2....1..0..3..1
..0..1..2..3....1..1..2..0....1..0..1..1....0..1..2..0....2..3..0..0
..3..2..3..1....1..1..0..1....1..1..1..2....1..2..0..2....3..1..0..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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