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A206981
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Number of n X 2 0..1 arrays avoiding the patterns 0 1 0 or 1 0 1 in any row, column, diagonal or antidiagonal.
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32
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4, 16, 36, 100, 256, 676, 1764, 4624, 12100, 31684, 82944, 217156, 568516, 1488400, 3896676, 10201636, 26708224, 69923044, 183060900, 479259664, 1254718084, 3284894596, 8599965696, 22515002500, 58945041796, 154320122896, 404015326884
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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) = 2*a(n-1) + 2*a(n-2) - a(n-3). G.f.: -4*x*(-1-2*x+x^2) / ( (1+x)*(x^2-3*x+1) ).
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EXAMPLE
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Some solutions for n=4
..1..1....0..0....0..0....0..0....1..1....0..1....1..1....0..1....1..0....0..0
..0..1....0..1....1..0....1..0....1..1....1..1....1..1....1..0....0..1....1..1
..0..0....1..1....1..1....1..0....1..1....1..0....1..1....1..0....0..1....1..1
..1..0....1..1....0..1....1..0....1..1....1..0....0..0....1..0....1..0....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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