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 A238111 #9 Feb 15 2019 16:09:11
%S A238111 2,4,12,44,180,788,3612,17116,83172,412196,2075436,10586892,54595476,
%T A238111 284157492,1490774076,7875206076,41854313412,223636052036,
%U A238111 1200637707852,6473448634348,35037238641780,190299310403924,1036863750837852,5665846701859484,31042935297750180,170499885177942628
%N A238111 Twice the large Schroeder numbers A006318.
%C A238111 Although this is simply twice A006318, it seems to arise often enough to warrant its own entry. See also A001003.
%H A238111 Li Guo and Jun Pei, <a href="http://arxiv.org/abs/1401.7386">Averaging algebras, Schroeder numbers and rooted trees</a>, arXiv preprint arXiv:1401.7386, 2014
%F A238111 G.f.: (1-x-sqrt(x^2-6*x+1))/x.
%t A238111 Table[-2 I Sqrt[2] LegendreP[n, -1, 2, 3], {n, 0, 25}] (* _Jean-François Alcover_, Feb 15 2019 *)
%Y A238111 Cf. A006318, A001003.
%K A238111 nonn
%O A238111 0,1
%A A238111 _N. J. A. Sloane_, Mar 04 2014