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 A081655 #19 Sep 08 2022 08:45:09
%S A081655 1,9,49,249,1249,6249,31249,156249,781249,3906249,19531249,97656249,
%T A081655 488281249,2441406249,12207031249,61035156249,305175781249,
%U A081655 1525878906249,7629394531249,38146972656249,190734863281249
%N A081655 2*5^n-1.
%C A081655 Binomial transform of A081654. Inverse binomial transform of A081656.
%H A081655 Vincenzo Librandi, <a href="/A081655/b081655.txt">Table of n, a(n) for n = 0..1000</a>
%H A081655 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-5).
%F A081655 G.f.: (1+3*x)/((1-5*x)*(1-x)).
%F A081655 E.g.f. 2*exp(5*x)-exp(x).
%F A081655 a(n) = 5*a(n-1)+4, with a(0)=1. - _Vincenzo Librandi_, Aug 01 2010
%t A081655 CoefficientList[Series[(1 + 3 x) / ((1 - 5 x) (1 - x)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Aug 10 2013 *)
%t A081655 NestList[5#+4&,1,30] (* _Harvey P. Dale_, Jul 04 2014 *)
%o A081655 (Magma) [2*5^n-1: n in [0..30]]; // _Vincenzo Librandi_, Aug 10 2013
%o A081655 (PARI) a(n)=2*5^n-1 \\ _Charles R Greathouse IV_, Sep 24 2015
%K A081655 easy,nonn
%O A081655 0,2
%A A081655 _Paul Barry_, Mar 26 2003