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 A133668 #17 Jan 02 2024 08:56:16
%S A133668 1,6,-30,-246,834,9690,-20334,-369174,362850,13653114,590514,
%T A133668 -490921590,-512180094,17160997146,35599480530,-582196416726,
%U A133668 -1863777715806,19095293286330,86191291055346,-601239267252534,-3704125745244990,17940487875846234
%N A133668 a(n) = a(n-1) - 36*a(n-2), a(0)=1, a(1)=6.
%H A133668 Matthew House, <a href="/A133668/b133668.txt">Table of n, a(n) for n = 0..1277</a>
%H A133668 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1,-36).
%F A133668 G.f.:(1+5*x)/(1-x+36*x^2).
%F A133668 a(n) = Sum_{k=0..n} A133607(n,k)*6^k. - _Philippe Deléham_, Dec 30 2007
%t A133668 CoefficientList[Series[(1+5x)/(1-x+36x^2),{x,0,40}],x] (* or *) LinearRecurrence[{1,-36},{1,6},40] (* _Harvey P. Dale_, Dec 28 2022 *)
%o A133668 (PARI) a(n)=([0,1; -36,1]^n*[1;6])[1,1] \\ _Charles R Greathouse IV_, Feb 15 2017
%K A133668 easy,sign
%O A133668 0,2
%A A133668 _Philippe Deléham_, Dec 28 2007
%E A133668 a(18) corrected by _Matthew House_, Feb 15 2017