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 A016204 #23 Feb 08 2024 03:14:21
%S A016204 1,12,115,1050,9481,85392,768655,6918150,62263861,560375772,
%T A016204 5043383995,45390460050,408514148641,3676627354152,33089646220135,
%U A016204 297806816046750,2680261344551821,24122352101228532,217101168911581075
%N A016204 Expansion of 1/((1-x)*(1-2*x)*(1-9*x)).
%H A016204 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (12,-29,18).
%F A016204 a(n) = (81*9^n-32*2^n+7)/56. - _Bruno Berselli_, Feb 09 2011
%F A016204 a(n) = 9*a(n-1) + 2^(n+1) - 1. - _Vincenzo Librandi_, Feb 09 2011
%F A016204 a(0)=1, a(1)=12, a(2)=115, a(n) = 12*a(n-1) - 29*a(n-2) + 18*a(n-3). - _Harvey P. Dale_, Jun 05 2012
%p A016204 A016204 := proc(n) (9^(n+2)-2^(n+5)+7)/56 ; end proc:
%p A016204 seq(A016204(n),n=0..20) ; # _R. J. Mathar_, Feb 09 2011
%t A016204 CoefficientList[Series[1/((1-x)(1-2x)(1-9x)),{x,0,40}],x] (* or *) LinearRecurrence[{12,-29,18},{1,12,115},40] (* _Harvey P. Dale_, Jun 05 2012 *)
%o A016204 (PARI) Vec(1/((1-x)*(1-2*x)*(1-9*x))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%K A016204 nonn,easy
%O A016204 0,2
%A A016204 _N. J. A. Sloane_