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 A013968 a(n) = sigma_20(n), the sum of the 20th powers of the divisors of n. 5
 1, 1048577, 3486784402, 1099512676353, 95367431640626, 3656161927895954, 79792266297612002, 1152922604119523329, 12157665462543713203, 100000095367432689202, 672749994932560009202, 3833763649708914645906, 19004963774880799438802, 83668335217551100221154 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If the canonical factorization of n into prime powers is the product of p^e(p) then sigma_k(n) = Product_p ((p^((e(p)+1)*k))-1)/(p^k-1). Sum_{d|n} 1/d^k is equal to sigma_k(n)/n^k. So sequences A017665-A017712 also give the numerators and denominators of sigma_k(n)/n^k for k = 1..24. The power sums sigma_k(n) are in sequences A000203 (k=1), A001157-A001160 (k=2,3,4,5), A013954-A013972 for k = 6,7,...,24. - Ahmed Fares (ahmedfares(AT)my-deja.com), Apr 05 2001 LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 Index entries for sequences related to sigma(n). FORMULA G.f.: Sum_{k>=1} k^20*x^k/(1-x^k). - Benoit Cloitre, Apr 21 2003 From Amiram Eldar, Oct 29 2023: (Start) Multiplicative with a(p^e) = (p^(20*e+20)-1)/(p^20-1). Dirichlet g.f.: zeta(s)*zeta(s-20). Sum_{k=1..n} a(k) = zeta(21) * n^21 / 21 + O(n^22). (End) MATHEMATICA DivisorSigma[20, Range[20]] (* Harvey P. Dale, Jul 26 2015 *) PROG (Sage) [sigma(n, 20)for n in range(1, 13)] # Zerinvary Lajos, Jun 04 2009 (PARI) vector(50, n, sigma(n, 20)) \\ G. C. Greubel, Nov 03 2018 (Magma) [DivisorSigma(20, n): n in [1..50]]; // G. C. Greubel, Nov 03 2018 CROSSREFS Cf. A000203, A001157-A001160, A013954-A013972, A017665-A017712. Sequence in context: A370255 A351316 A017703 * A036098 A203668 A253312 Adjacent sequences: A013965 A013966 A013967 * A013969 A013970 A013971 KEYWORD nonn,easy,mult AUTHOR N. J. A. Sloane STATUS approved

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Last modified June 16 19:52 EDT 2024. Contains 373432 sequences. (Running on oeis4.)