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 A034663 #28 Jul 08 2025 21:26:17
%S A034663 4,32,500,9632,196964,4101152,85884500,1801914272,37828630724,
%T A034663 794320419872,16680163512500,350279478046112,7355841353205284,
%U A034663 154472474629724192,3243920610749364500,68122323330527541152
%N A034663 Sum of n-th powers of divisors of 21.
%H A034663 T. D. Noe, <a href="/A034663/b034663.txt">Table of n, a(n) for n=0..200</a>
%H A034663 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (32,-262,672,-441).
%F A034663 a(n) = (1+3^n)*(1+7^n). - _Bruno Berselli_, Apr 17 2014
%F A034663 G.f.: -4*(168*x^3-131*x^2+24*x-1) / ((x-1)*(3*x-1)*(7*x-1)*(21*x-1)). - _Colin Barker_, May 03 2014
%t A034663 Total[#^Range[0, 20]&/@Divisors[21]] (* _Vincenzo Librandi_, Apr 17 2014 *)
%t A034663 Table[(1 + 3^n) (1 + 7^n), {n, 0, 20}] (* _Bruno Berselli_, Apr 17 2014 *)
%o A034663 (Sage) [sigma(21,n)for n in range(0,16)] # _Zerinvary Lajos_, Jun 04 2009
%o A034663 (Magma) [DivisorSigma(n,21): n in [0..15]]; // _Vincenzo Librandi_, Apr 17 2014
%o A034663 (PARI) s=[]; for(n=0, 30, s=concat(s, sigma(21, n))); s \\ _Colin Barker_, May 03 2014
%K A034663 nonn,easy
%O A034663 0,1
%A A034663 _N. J. A. Sloane_