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A269771
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Number of length-n 0..3 arrays with every repeated value unequal to the previous repeated value plus one mod 3+1.
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1
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4, 16, 64, 252, 984, 3816, 14724, 56592, 216864, 829116, 3164184, 12058632, 45904644, 174598416, 663634944, 2521077372, 9573268824, 36340434216, 137913296004, 523277751312, 1985122823904, 7529850771516, 28558867923864
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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) = 6*a(n-1) - 6*a(n-2) - 9*a(n-3).
Empirical g.f.: 4*x*(1 - 2*x - 2*x^2) / ((1 - 3*x)*(1 - 3*x - 3*x^2)). - Colin Barker, Jan 28 2019
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EXAMPLE
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Some solutions for n=8:
..1. .3. .2. .3. .3. .1. .2. .0. .2. .0. .3. .3. .3. .2. .3. .1
..0. .0. .1. .1. .2. .3. .0. .2. .3. .3. .3. .3. .0. .1. .0. .0
..1. .0. .3. .1. .3. .0. .3. .2. .0. .2. .0. .1. .1. .2. .1. .0
..2. .3. .3. .1. .3. .2. .1. .2. .2. .2. .1. .0. .0. .0. .0. .1
..3. .3. .3. .1. .1. .1. .2. .2. .0. .1. .1. .1. .3. .0. .1. .0
..1. .1. .1. .1. .1. .1. .3. .3. .2. .0. .0. .2. .0. .1. .1. .0
..3. .0. .0. .1. .3. .1. .0. .0. .2. .0. .3. .0. .0. .2. .1. .0
..0. .1. .2. .2. .2. .0. .3. .3. .3. .3. .2. .1. .0. .2. .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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