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 A133666 #15 Jan 02 2024 08:55:31
%S A133666 1,4,-12,-76,116,1332,-524,-21836,-13452,335924,551156,-4823628,
%T A133666 -13642124,63535924,281809908,-734764876,-5243723404,6512514612,
%U A133666 90412089076,-13788144716,-1460381569932,-1239771254476,22126333864436,41962673936052
%N A133666 a(n) = a(n-1) - 16*a(n-2), a(0)=1, a(1)=4.
%H A133666 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1, -16).
%F A133666 G.f.: (1+3*x) / (1-x+16*x^2).
%F A133666 a(n) = Sum_{k=0..n} A133607(n,k)*4^k. - _Philippe Deléham_, Dec 29 2007
%K A133666 easy,sign
%O A133666 0,2
%A A133666 _Philippe Deléham_, Dec 28 2007, corrected Jan 04 2008
%E A133666 a(19) corrected and more terms from _Sean A. Irvine_, May 19 2019