This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A091986 #16 Jul 15 2025 00:19:42
%S A091986 1,9,73,252,585,1134,2044,3096,4681,6813,9198,11988,16380,19782,25112,
%T A091986 31752,37449,44226,55261,61740,73710,86688,97236,109512,131068,141759,
%U A091986 160454,183960,201240,219510,257544,268128,299593,335664,358722,390096,442845
%N A091986 a(0)=1, a(n) = sigma_3(2n).
%F A091986 Sum_{k=1..n} a(k) ~ (17*zeta(4)/8) * n^4. - _Amiram Eldar_, Dec 12 2023
%F A091986 G.f.: 1 + Sum_{k>=1} k^3*x^(lcm(k, 2)/2)/(1 - x^(lcm(k, 2)/2)). - _Miles Wilson_, Jul 10 2025
%t A091986 Join[{1},Table[DivisorSigma[3,n],{n,2,80,2}]] (* _Harvey P. Dale_, Feb 26 2011 *)
%o A091986 (PARI) a(n) = if(n < 1, 1, sigma(2*n, 3)); \\ _Amiram Eldar_, Dec 12 2023
%Y A091986 Bisection of A001158.
%Y A091986 Cf. A013662, A045823.
%K A091986 nonn,easy
%O A091986 0,2
%A A091986 _N. J. A. Sloane_, Mar 20 2004