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A268989
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Number of n X 2 binary arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once.
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1
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4, 13, 41, 126, 379, 1121, 3272, 9449, 27049, 76866, 217079, 609793, 1705036, 4748101, 13174889, 36440646, 100503667, 276476129, 758785424, 2078056481, 5680052329, 15497929098, 42216552431, 114824352001, 311871557524
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3) - a(n-4).
Empirical g.f.: x*(4 - 11*x + 7*x^2 - x^3) / (1 - 3*x + x^2)^2. - Colin Barker, Jan 17 2019
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EXAMPLE
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Some solutions for n=4:
..1..0. .1..1. .1..0. .0..0. .1..0. .1..1. .0..0. .1..0. .0..0. .1..1
..0..1. .0..0. .0..1. .1..0. .1..0. .0..0. .0..0. .0..0. .1..0. .0..1
..0..1. .1..0. .0..0. .1..0. .0..0. .1..0. .0..1. .1..0. .0..0. .0..0
..1..0. .1..0. .1..0. .0..1. .0..1. .0..0. .1..0. .0..1. .1..1. .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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