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 A081657 #21 Sep 08 2022 08:45:09
%S A081657 1,11,89,659,4721,33371,234569,1644899,11523041,80687531,564891449,
%T A081657 3954476339,27682042961,193776426491,1356441362729,9495108670979,
%U A081657 66465818092481,465260898834251,3256826808400409,22797789208484819
%N A081657 2*7^n-3^n.
%C A081657 Binomial transform of A081656.
%H A081657 Vincenzo Librandi, <a href="/A081657/b081657.txt">Table of n, a(n) for n = 0..1000</a>
%H A081657 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10,-21).
%F A081657 G.f.: (1+x)/((1-7*x)*(1-3*x)).
%F A081657 E.g.f. 2*exp(7*x)-exp(3*x).
%F A081657 a(0)=0, a(1)=11; for n>1, a(n) = 10*a(n-1) -21*a(n-2). - _Vincenzo Librandi_ Aug 10 2013
%t A081657 CoefficientList[Series[(1 + x) / ((1 - 7 x) (1 - 3 x)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Aug 10 2013 *)
%o A081657 (Magma) [2*7^n-3^n: n in [0..30]]; // _Vincenzo Librandi_, Dec 05 2012
%K A081657 easy,nonn
%O A081657 0,2
%A A081657 _Paul Barry_, Mar 26 2003