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A116156
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a(n) = 5^n * n*(n + 1).
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1
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0, 10, 150, 1500, 12500, 93750, 656250, 4375000, 28125000, 175781250, 1074218750, 6445312500, 38085937500, 222167968750, 1281738281250, 7324218750000, 41503906250000, 233459472656250, 1304626464843750, 7247924804687500
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OFFSET
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0,2
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LINKS
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FORMULA
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Sum_{n>=1} 1/a(n) = 1 - 4*log(5/4).
Sum_{n>=1} (-1)^(n+1)/a(n) = 6*log(6/5) - 1. (End)
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MATHEMATICA
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Table[(n^2 + n) 5^n, {n, 0, 30}] (* or *) CoefficientList[Series[10 x/(1 - 5 x)^3, {x, 0, 30}], x](* Vincenzo Librandi, Feb 28 2013 *)
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PROG
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(Magma) [(n^2+n)*5^n: n in [0..30]]; /* or */ I:=[0, 10, 150]; [n le 3 select I[n] else 15*Self(n-1)-75*Self(n-2)+125*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Feb 28 2013
(Sage) [5^n*n*(n+1) for n in (0..30)] # G. C. Greubel, May 10 2019
(GAP) List([0..30], n-> 5^n*n*(n+1)) # G. C. Greubel, May 10 2019
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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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