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A243383
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Number of length n+3 0..2 arrays with no four elements in a row with pattern abba (with a!=b) and new values 0..2 introduced in 0..2 order.
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1
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13, 35, 96, 265, 733, 2029, 5618, 15557, 43081, 119303, 330384, 914929, 2533705, 7016569, 19430930, 53809925, 149015413, 412667243, 1142796240, 3164736889, 8764081669, 24270304357, 67211568290, 186128482181, 515444182609
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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) = 4*a(n-1) - 4*a(n-2) + 2*a(n-3) - a(n-4).
Empirical g.f.: x*(13 - 17*x + 8*x^2 - 5*x^3) / ((1 - x)*(1 - 3*x + x^2 - x^3)). - Colin Barker, Nov 02 2018
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EXAMPLE
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Some solutions for n=3:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....1....0....1....1....1....0....1....1....1....0....0....0....0
..0....1....1....0....1....2....0....1....0....0....0....2....1....1....1....1
..1....2....1....2....0....0....2....1....1....2....2....2....2....2....0....2
..0....2....2....0....1....2....1....1....2....1....1....2....1....0....2....1
..1....2....2....0....0....0....0....2....0....1....2....0....0....0....2....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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