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A210896
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Number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order
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0
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1, 2, 20, 400, 16716, 1444348, 258951340, 96266852004, 74214689922928, 118642250445743920, 393305989512539553728, 2703723885515478100466476, 38542035415959856159523945096
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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=3
..0..1..0....0..1..1....0..1..0....0..1..0....0..1..0....0..1..0....0..1..0
..1..2..0....1..0..2....1..0..2....1..2..1....1..0..1....1..0..2....1..2..0
..0..0..1....1..2..0....0..2..1....0..1..0....0..1..0....0..2..0....0..0..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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