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 A221949 #14 Nov 29 2018 10:36:07
%S A221949 0,1,1,2,5,12,26,53,104,199,375,700,1299,2402,4432,8167,15038,27677,
%T A221949 50925,93686,172337,317000,583078,1072473,1972612,3628227,6673379,
%U A221949 12274288,22575967,41523710,76374044,140473803,258371642,475219577,874065113,1607656426,2956941213,5438662852,10003260594,18398864765,33840788320,62242913791,114482566991
%N A221949 Expansion of (-x+2*x^2-x^3-x^4-2*x^5)/(-1+3*x-2*x^2-x^4+x^5).
%H A221949 M. Dairyko, S. Tyner, L. Pudwell and C. Wynn, <a href="http://arxiv.org/abs/1203.0795">Non-contiguous pattern avoidance in binary trees</a>, 2012, arXiv:1203.0795 [math.CO], p. 18 (Class F).
%H A221949 Michael Dairyko, Lara Pudwell, Samantha Tyner, Casey Wynn, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v19i3p22">Non-contiguous pattern avoidance in binary trees</a>. Electron. J. Combin. 19 (2012), no. 3, Paper 22, 21 pp. MR2967227.
%H A221949 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2,0,-1,1).
%F A221949 G.f.: x*(1-2*x+x^2+x^3+2*x^4)/((1-x)^2*(1-x-x^2-x^3)).
%t A221949 Join[{0},LinearRecurrence[{3,-2,0,-1,1},{1,1,2,5,12},50]] (* _Harvey P. Dale_, Nov 12 2014 *)
%t A221949 CoefficientList[Series[x*(1-2*x+x^2+x^3+2*x^4)/((1-x)^2*(1-x-x^2-x^3)) , {x, 0, 50}], x] (* _Stefano Spezia_, Nov 29 2018 *)
%K A221949 nonn,easy
%O A221949 0,4
%A A221949 _N. J. A. Sloane_, Feb 01 2013