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 A021684 #18 Jul 08 2025 08:47:30
%S A021684 1,23,360,4810,59111,690573,7801990,86089520,933531621,9989073523,
%T A021684 105774639620,1110701801430,11583617458531,120125571974873,
%U A021684 1239860303429250,12746044308940540,130587414625807841
%N A021684 Expansion of 1/((1-x)(1-3x)(1-9x)(1-10x)).
%H A021684 Vincenzo Librandi, <a href="/A021684/b021684.txt">Table of n, a(n) for n = 0..200</a>
%H A021684 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (23,-169,417,-270)
%F A021684 a(n) = -1/144 +10^(n+3)/63+3^(n+2)/28 -3*9^(n+2)/16. - R. J. Mathar, Mar 15 2011
%t A021684 CoefficientList[Series[1 / ((1 - x) (1 - 3 x) (1 - 9 x) (1 - 10 x)), {x, 0, 20}], x] (* _Vincenzo Librandi_, Jul 11 2013 *)
%t A021684 LinearRecurrence[{23,-169,417,-270},{1,23,360,4810},30] (* _Harvey P. Dale_, Nov 18 2018 *)
%o A021684 (PARI) Vec(1/((1-x)*(1-3*x)*(1-9*x)*(1-10*x))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%K A021684 nonn,easy
%O A021684 0,2
%A A021684 _N. J. A. Sloane_