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A207846
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Number of 3 X n 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 0 and 1 1 1 vertically.
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1
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6, 36, 72, 180, 432, 1044, 2520, 6084, 14688, 35460, 85608, 206676, 498960, 1204596, 2908152, 7020900, 16949952, 40920804, 98791560, 238503924, 575799408, 1390102740, 3356004888, 8102112516, 19560229920, 47222572356, 114005374632
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + a(n-2) for n>3.
G.f.: 6*x*(1 + 4*x - x^2) / (1 - 2*x - x^2).
a(n) = 9*(sqrt(2)*((1-sqrt(2))^n*(1+sqrt(2)) + (-1+sqrt(2))*(1+sqrt(2))^n)) for n>2.
(End)
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EXAMPLE
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Some solutions for n=4:
..1..1..1..1....1..1..0..0....1..1..0..1....1..0..1..1....0..1..0..0
..0..1..0..0....1..0..1..1....0..1..1..1....1..1..0..0....1..0..1..1
..1..0..1..1....0..1..1..0....1..0..1..0....0..1..1..0....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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