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A243028
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Number of length n+3 0..3 arrays with no four elements in a row with pattern abba (possibly a=b) and new values 0..3 introduced in 0..3 order.
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1
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13, 42, 147, 536, 1987, 7414, 27736, 103868, 389129, 1458054, 5463618, 20473754, 76721788, 287502448, 1077370309, 4037278442, 15129079265, 56693899710, 212451684345, 796130077586, 2983375282018, 11179741027060, 41894363838109
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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) - a(n-2) + 2*a(n-3) - 6*a(n-4) - 2*a(n-5) - 3*a(n-6).
Empirical g.f.: x*(13 - 10*x - 8*x^2 - 36*x^3 - 16*x^4 - 14*x^5) / ((1 - x - x^3)*(1 - 3*x - 2*x^2 - 3*x^3)). - Colin Barker, Nov 01 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
..1....1....0....0....1....1....0....1....0....1....1....1....1....0....1....0
..2....0....1....1....0....2....0....1....0....2....0....0....0....0....0....1
..2....2....0....2....0....3....1....1....1....0....1....2....2....1....1....2
..3....3....0....3....2....2....2....0....0....1....0....0....3....2....1....1
..0....0....0....3....0....2....3....1....2....2....2....0....2....0....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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