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A027823
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a(n) = 77*(n+1)*binomial(n+6,11).
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1
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462, 6468, 48048, 252252, 1051050, 3699696, 11435424, 31855824, 81477396, 193993800, 434546112, 923410488, 1873980108, 3651858672, 6864396000, 12493200720, 22086194130, 38030772780, 63935791920, 105157552500, 169513974630, 268241893920, 417265168320
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OFFSET
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5,1
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COMMENTS
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Number of 18-subsequences of [ 1, n ] with just 6 contiguous pairs.
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (13,-78,286,-715,1287,-1716,1716,-1287,715,-286,78,-13,1).
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FORMULA
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G.f.: 462*(1+x)*x^5/(1-x)^13.
Sum_{n>=5} 1/a(n) = 10446403/176400 - 6*Pi^2.
Sum_{n>=5} (-1)^(n+1)/a(n) = 3*Pi^2 - 82899/2800. (End)
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MATHEMATICA
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Table[77(n+1) Binomial[n+6, 11], {n, 5, 40}] (* or *) LinearRecurrence[{13, -78, 286, -715, 1287, -1716, 1716, -1287, 715, -286, 78, -13, 1}, {462, 6468, 48048, 252252, 1051050, 3699696, 11435424, 31855824, 81477396, 193993800, 434546112, 923410488, 1873980108}, 30] (* Harvey P. Dale, Oct 20 2016 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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