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 A133642 #16 Jan 02 2024 08:55:22
%S A133642 1,4,32,208,1472,10048,69632,479488,3310592,22832128,157540352,
%T A133642 1086803968,7498022912,51728171008,356873142272,2462055989248,
%U A133642 16985686802432,117183866994688,808449204027392,5577474156003328,38478880704561152,265465005938311168
%N A133642 a(n) = 4*a(n-1)+20*a(n-2) for n>=3, a(0)=1, a(1)=4, a(2)=32.
%H A133642 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,20).
%F A133642 G.f.: (1-4*x^2)/(1-4*x-20*x^2).
%F A133642 a(n) = Sum_{k=0..n} A122950(n,k)*4^k.
%Y A133642 Cf. A122950.
%K A133642 easy,nonn
%O A133642 0,2
%A A133642 _Philippe Deléham_, Dec 31 2007
%E A133642 a(15) corrected by _Georg Fischer_, Mar 13 2020