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%I #26 Sep 08 2022 08:44:52
%S 4,32,500,9632,196964,4101152,85884500,1801914272,37828630724,
%T 794320419872,16680163512500,350279478046112,7355841353205284,
%U 154472474629724192,3243920610749364500,68122323330527541152
%N Sum of n-th powers of divisors of 21.
%H T. D. Noe, <a href="/A034663/b034663.txt">Table of n, a(n) for n=0..200</a>
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (32,-262,672,-441).
%F a(n) = (1+3^n)*(1+7^n). - _Bruno Berselli_, Apr 17 2014
%F 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 Total[#^Range[0, 20]&/@Divisors[21]] (* _Vincenzo Librandi_, Apr 17 2014 *)
%t Table[(1 + 3^n) (1 + 7^n), {n, 0, 20}] (* _Bruno Berselli_, Apr 17 2014 *)
%o (Sage) [sigma(21,n)for n in range(0,16)] # _Zerinvary Lajos_, Jun 04 2009
%o (Magma) [DivisorSigma(n,21): n in [0..15]]; // _Vincenzo Librandi_, Apr 17 2014
%o (PARI) s=[]; for(n=0, 30, s=concat(s, sigma(21, n))); s \\ _Colin Barker_, May 03 2014
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_.