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A212824
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Number of 0..3 arrays of length n with no adjacent pair equal to its immediately preceding adjacent pair, and new values introduced in 0..3 order.
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1
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1, 2, 5, 13, 43, 152, 559, 2091, 7882, 29809, 112895, 427824, 1621691, 6147791, 23307226, 88363077, 335007715, 1270107208, 4815336407, 18256317315, 69214939274, 262413734345, 994885963543, 3771899000928, 14300354743363
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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) + a(n-2) - 6*a(n-3) - 3*a(n-4) for n>7.
Empirical g.f.: x*(1 + x + x^2)*(1 - 3*x - 2*x^2 + 2*x^3 + x^4) / ((1 - x - x^2)*(1 - 3*x - 3*x^2)). - Colin Barker, Jul 21 2018
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EXAMPLE
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Some solutions for n=8:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....1....1....1....1....1....1....1....1....0....1....1....1....0....1....1
..1....2....0....1....0....1....2....2....1....1....1....2....2....1....1....2
..2....3....2....2....2....2....0....0....2....2....0....3....2....2....0....2
..2....0....0....2....2....2....3....2....2....3....2....2....2....3....1....3
..0....2....3....3....3....0....2....1....0....1....3....1....0....3....1....1
..1....2....2....3....1....0....2....0....2....2....3....3....3....2....1....0
..1....0....1....2....0....0....1....3....3....0....2....1....0....0....2....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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