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 A265107 #21 Nov 02 2021 04:33:55
%S A265107 0,1,2,6,16,38,92,222,536,1294,3124,7542,18208,43958,106124,256206,
%T A265107 618536,1493278,3605092,8703462,21012016,50727494,122467004,295661502,
%U A265107 713790008,1723241518,4160273044,10043787606,24247848256,58539484118,141326816492,341193117102
%N A265107 Expansion of (2*x^4+x^3+x)/(-x^2-2*x+1).
%H A265107 Colin Barker, <a href="/A265107/b265107.txt">Table of n, a(n) for n = 0..1000</a>
%H A265107 M. Diepenbroek, M. Maus and A. Stoll, <a href="http://www.valpo.edu/mathematics-statistics/files/2014/09/Pudwell2015.pdf">Pattern Avoidance in Reverse Double Lists</a>, Preprint 2015. See Table 3.
%H A265107 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,1).
%F A265107 From _Colin Barker_, Apr 12 2016: (Start)
%F A265107 a(n) = ((1+sqrt(2))^n*(-5+4*sqrt(2)) + (1-sqrt(2))^n*(5+4*sqrt(2)))/sqrt(2) for n>2.
%F A265107 a(n) = 2*a(n-1)+a(n-2) for n>4.
%F A265107 (End)
%t A265107 Join[{0, 1, 2}, LinearRecurrence[{2, 1}, {6, 16}, 30]] (* _Jean-François Alcover_, Nov 02 2021 *)
%o A265107 (PARI) concat(0, Vec(x*(1+x)*(1-x+2*x^2)/(1-2*x-x^2) + O(x^50))) \\ _Colin Barker_, Apr 12 2016
%Y A265107 Cf. A002605, A265106, A265278, A270810.
%K A265107 nonn,easy
%O A265107 0,3
%A A265107 _Alois P. Heinz_, Apr 06 2016