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a(n) = sigma_2(3*n).
3

%I #19 Dec 12 2023 08:00:57

%S 10,50,91,210,260,455,500,850,820,1300,1220,1911,1700,2500,2366,3410,

%T 2900,4100,3620,5460,4550,6100,5300,7735,6510,8500,7381,10500,8420,

%U 11830,9620,13650,11102,14500,13000,17220,13700,18100,15470,22100,16820,22750,18500

%N a(n) = sigma_2(3*n).

%H Seiichi Manyama, <a href="/A283237/b283237.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A001157(3*n).

%F Sum_{k=1..n} a(k) ~ (29*zeta(3)/9) * n^3. - _Amiram Eldar_, Dec 12 2023

%t Table[DivisorSigma[2,3n],{n,1,43}] (* _Indranil Ghosh_, Mar 03 2017 *)

%o (PARI) a(n) = sigma(3*n,2); \\ _Indranil Ghosh_, Mar 03 2017

%Y Sigma_2(k*n): A001157 (k=1), A099979 (k=2), this sequence (k=3).

%Y Cf. A002117.

%K nonn,easy

%O 1,1

%A _Seiichi Manyama_, Mar 03 2017