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A269614
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Number of length-n 0..3 arrays with no repeated value differing from the previous repeated value by other than plus two, zero or minus 1.
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1
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4, 16, 64, 249, 954, 3611, 13544, 50442, 186822, 688899, 2531406, 9275757, 33912330, 123759252, 450985950, 1641487455, 5969001906, 21688869249, 78760649178, 285872602590, 1037218320720, 3762161399673, 13642773106086, 49463937282915
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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) = 12*a(n-1) - 51*a(n-2) + 81*a(n-3) - 3*a(n-4) - 63*a(n-5) - 24*a(n-6) - 9*a(n-7).
Empirical g.f.: x*(4 - 32*x + 76*x^2 - 27*x^3 - 54*x^4 - 22*x^5 - 7*x^6) / ((1 - 3*x)*(1 - 9*x + 24*x^2 - 9*x^3 - 24*x^4 - 9*x^5 - 3*x^6)). - Colin Barker, Jan 25 2019
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EXAMPLE
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Some solutions for n=8:
..0. .3. .2. .3. .1. .0. .0. .0. .2. .2. .2. .3. .2. .2. .2. .3
..3. .3. .1. .3. .3. .2. .2. .2. .0. .3. .1. .1. .1. .3. .2. .0
..3. .0. .3. .2. .2. .1. .0. .3. .1. .3. .3. .3. .2. .0. .2. .0
..2. .3. .2. .2. .1. .3. .0. .3. .0. .1. .2. .2. .1. .0. .1. .2
..3. .2. .3. .2. .0. .2. .1. .0. .1. .0. .0. .3. .3. .1. .3. .0
..1. .2. .3. .1. .0. .3. .2. .3. .3. .3. .0. .2. .1. .2. .1. .2
..0. .1. .0. .3. .3. .3. .0. .2. .0. .3. .2. .3. .2. .0. .0. .0
..3. .0. .2. .0. .1. .1. .2. .3. .2. .1. .3. .3. .1. .0. .3. .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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