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A207165
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Number of n X 4 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 0 1 and 1 0 1 vertically.
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1
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9, 81, 261, 603, 1161, 1989, 3141, 4671, 6633, 9081, 12069, 15651, 19881, 24813, 30501, 36999, 44361, 52641, 61893, 72171, 83529, 96021, 109701, 124623, 140841, 158409, 177381, 197811, 219753, 243261, 268389, 295191, 323721, 354033, 386181
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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) = 9*n^3 + 9*n - 9.
G.f.: 9*x*(1 + 5*x - x^2 + x^3) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4.
(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..0....0..0..1..1....1..0..0..1
..0..1..1..1....0..1..0..0....0..0..1..0....1..0..0..1....0..1..1..0
..0..1..1..0....0..1..0..0....0..0..1..0....1..0..0..1....0..0..1..0
..0..0..1..0....0..1..0..0....0..0..1..0....1..0..0..1....0..0..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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