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A202900
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Number of n X 2 0..1 arrays with every one equal to some NW, E or S neighbor.
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1
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1, 4, 14, 40, 116, 344, 1016, 2992, 8816, 25984, 76576, 225664, 665024, 1959808, 5775488, 17020160, 50157824, 147813376, 435600896, 1283700736, 3783021568, 11148433408, 32854046720, 96819736576, 285324406784, 840841134080
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 4*a(n-1) -4*a(n-2) +4*a(n-3) -4*a(n-4).
Empirical g.f.: x*(1 + 2*x^2 - 4*x^3) / (1 - 4*x + 4*x^2 - 4*x^3 + 4*x^4). - Colin Barker, Jun 02 2018
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EXAMPLE
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Some solutions for n=5:
..1..1....0..0....1..1....1..0....0..1....1..0....1..0....1..1....1..0....1..1
..0..1....0..0....1..1....1..0....0..1....1..1....1..0....0..1....1..1....1..1
..0..0....1..0....0..0....1..1....0..1....1..1....1..0....1..1....0..0....0..1
..1..1....1..1....1..0....0..1....1..1....0..1....1..0....1..1....1..1....1..1
..1..1....0..1....1..1....0..0....1..1....0..0....1..1....0..1....1..1....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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