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A268460
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Number of length-6 0..n arrays with no adjacent pair x,x+1 followed at any distance by x+1,x.
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1
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22, 456, 3146, 13204, 41526, 108032, 245626, 504876, 959414, 1712056, 2901642, 4710596, 7373206, 11184624, 16510586, 23797852, 33585366, 46516136, 63349834, 84976116, 112428662, 146899936, 189756666, 242556044, 307062646, 385266072
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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) = n^6 + 6*n^5 + 11*n^4 + 2*n^3 + 6*n - 4.
G.f.: 2*x*(11 + 151*x + 208*x^2 - 6*x^3 - 13*x^4 + 11*x^5 - 2*x^6) / (1 - x)^7.
a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.
(End)
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EXAMPLE
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Some solutions for n=6:
2 0 2 3 6 4 4 4 3 2 3 6 0 3 1 2
5 2 6 2 3 2 2 2 2 4 1 0 5 2 5 6
2 4 4 6 4 4 5 1 2 4 1 4 4 2 0 0
0 0 0 4 6 1 4 2 4 2 3 0 5 0 3 0
0 4 3 4 1 0 2 4 4 3 6 5 5 0 5 1
6 2 0 5 0 1 2 5 6 4 5 6 1 2 2 2
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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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