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A162258
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a(n) = (2*n^3 + 5*n^2 - 9*n)/2.
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1
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-1, 9, 36, 86, 165, 279, 434, 636, 891, 1205, 1584, 2034, 2561, 3171, 3870, 4664, 5559, 6561, 7676, 8910, 10269, 11759, 13386, 15156, 17075, 19149, 21384, 23786, 26361, 29115, 32054, 35184, 38511, 42041, 45780, 49734, 53909, 58311, 62946, 67820
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OFFSET
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1,2
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LINKS
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FORMULA
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Row sums from A155546: a(n) = Sum_{m=1..n} (2*m*n + m + n - 5).
G.f.: x*(-1 + 13*x - 6*x^2)/(1-x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). (End)
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MATHEMATICA
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LinearRecurrence[{4, -6, 4, -1}, {-1, 9, 36, 86}, 50] (* or *) CoefficientList[Series[(2+7*x-3*x^2)/(1-x)^4, {x, 0, 50}], x] (* Vincenzo Librandi, Mar 04 2012 *)
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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