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 A353581 #16 Jul 09 2022 11:11:32 %S A353581 0,0,2,1,2,8,20,45,108,264,638,1537,3710,8960,21632,52221,126072, %T A353581 304368,734810,1773985,4282778,10339544,24961868,60263277,145488420, %U A353581 351240120,847968662,2047177441,4942323542,11931824528,28805972600,69543769725,167893512048,405330793824 %N A353581 a(n) = 2*a(n-1) + 2*a(n-3) + a(n-4), with a(0) = 0 = a(1), a(2) = 2, and a(3) = 1. %H A353581 Paul K. Stockmeyer, <a href="/A353581/b353581.txt">Table of n, a(n) for n = 0..1000</a> %H A353581 Andreas M. Hinz and Paul K. Stockmeyer, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL25/Hinz/hinz5.html">Precious Metal Sequences and Sierpinski-Type Graphs</a>, J. Integer Seq., Vol 25 (2022), Article 22.4.8. %H A353581 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,2,1). %F A353581 a(n) = (1/8) ((5-3*s)*(1+s)^n + (5+3*s)*(1-s)^n + 2*sin(n*Pi/2) - 10*cos(n*Pi/2)) where s = sqrt(2). %F A353581 G.f.: x^2*(2 - 3*x)/((1 + x^2)*(1 - 2*x - x^2)). - _Stefano Spezia_, May 04 2022 %K A353581 nonn,easy %O A353581 0,3 %A A353581 _Paul K. Stockmeyer_, May 04 2022