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A130861
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a(n) = (n-1)*(2*n+5).
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18
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0, 9, 22, 39, 60, 85, 114, 147, 184, 225, 270, 319, 372, 429, 490, 555, 624, 697, 774, 855, 940, 1029, 1122, 1219, 1320, 1425, 1534, 1647, 1764, 1885, 2010, 2139, 2272, 2409, 2550, 2695, 2844, 2997, 3154, 3315, 3480, 3649, 3822, 3999, 4180, 4365
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OFFSET
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1,2
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COMMENTS
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Old name was: "Ratio of Sum of k^2-1 to sum of k made into an integer sequence: (n-1)*(2*n+5)".
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LINKS
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FORMULA
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a(n) = 3*(n + 1)*( Sum_{k=1..n} k^2-1 )/ ( Sum_{k=1..n} k ) = (-1 + n)*(5 + 2*n).
E.g.f.: 5 + (2*x^2 + 5* x -5)*exp(x). - G. C. Greubel, Jul 21 2017
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MATHEMATICA
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Table[(n-1)(2n+5), {n, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 9, 22}, 50] (* Harvey P. Dale, Oct 02 2015 *)
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PROG
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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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