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Sum of divisors of cubes.
15

%I #49 Oct 25 2023 14:16:24

%S 1,15,40,127,156,600,400,1023,1093,2340,1464,5080,2380,6000,6240,8191,

%T 5220,16395,7240,19812,16000,21960,12720,40920,19531,35700,29524,

%U 50800,25260,93600,30784,65535,58560,78300,62400,138811,52060,108600,95200

%N Sum of divisors of cubes.

%C The Mobius transform of the sequence is 1, 14, 39 ,112, 155,..., which equals the sequence defined by n*A160889(n). - _R. J. Mathar_, Apr 15 2011

%C _Zhi-Wei Sun_ noted that the first 10^7 terms are pairwise distinct, but _Noam D. Elkies_ found that a(48142241) = a(48374911), a(384422506) = a(403764207) and so on. - _Zhi-Wei Sun_, Jan 08 2014

%H Seiichi Manyama, <a href="/A175926/b175926.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000203(n^3). - _R. J. Mathar_, Mar 31 2011

%F Multiplicative with a(p^e) = (p^(3e+1)-1)/(p-1). - _R. J. Mathar_, Mar 31 2011

%F Sum_{k>=1} 1/a(k) = 1.11535899887110289127674868460900333554265894187008102863022551119560512446... - _Vaclav Kotesovec_, Sep 20 2020

%F Sum_{k=1..n} a(k) ~ c * n^4, where c = (zeta(4)/4) * Product_{p prime} (1 + 1/p^2 + 1/p^3) = 0.4732277044... . - _Amiram Eldar_, Nov 05 2022

%t DivisorSigma[1,#]&/@((Range[40])^3) (* _Harvey P. Dale_, Aug 30 2015 *)

%t f[p_, e_] := (p^(3*e + 1) - 1)/(p - 1); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 50] (* _Amiram Eldar_, Sep 10 2020 *)

%o (Magma) [ SumOfDivisors(n^3) : n in [1..100]]; // _Vincenzo Librandi_, Apr 14 2011

%o (PARI) a(n) = sigma(n^3); \\ _Amiram Eldar_, Nov 05 2022

%o (Python)

%o from math import prod

%o from sympy import factorint

%o def A175926(n): return prod((p**(3*e+1)-1)//(p-1) for p,e in factorint(n).items()) # _Chai Wah Wu_, Oct 25 2023

%Y Cf. sigma(n^k): A000203 (k=1), A065764 (k=2), this sequence (k=3), A202994 (k=4), A203556 (k=5).

%Y Cf. A000578, A013662, A160889.

%K nonn,mult

%O 1,2

%A _Zak Seidov_, Oct 19 2010