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 A121720 #27 Jun 04 2025 16:25:09
%S A121720 0,1,1,3,4,10,14,34,48,116,164,396,560,1352,1912,4616,6528,15760,
%T A121720 22288,53808,76096,183712,259808,627232,887040,2141504,3028544,
%U A121720 7311552,10340096,24963200,35303296,85229696,120532992,290992384,411525376,993510144,1405035520
%N A121720 a(n) = 4*a(n-2) - 2*a(n-4).
%C A121720 For n>1, number of walks of length n-2 on the 5-vertex graph with edges {{0,1}, {1,2}, {2,3}, {2,4}} starting at vertex 3. - _Sean A. Irvine_, Jun 03 2025
%H A121720 Sean A. Irvine, <a href="https://oeis.org/wiki/User:Sean_A._Irvine/Walks_on_Graphs#5_vertices">Walks on Graphs</a>.
%H A121720 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-2).
%F A121720 a(n) = A007068(n-2), n>2.
%F A121720 G.f.: -x^2*(-1-x+x^2)/(1-4*x^2+2*x^4). [Oct 14 2009]
%t A121720 LinearRecurrence[{0,4,0,-2},{0,1,1,3},30] (* _Harvey P. Dale_, May 21 2014 *)
%Y A121720 Cf A002530, A048788.
%Y A121720 Essentially the same as A007068.
%K A121720 nonn,easy
%O A121720 1,4
%A A121720 _Roger L. Bagula_ and _Gary W. Adamson_, Sep 07 2006
%E A121720 Definition replaced by recurrence - The Assoc. Editors of the OEIS, Oct 14 2009
%E A121720 More terms from _Harvey P. Dale_, May 21 2014