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 A291887 #7 Sep 09 2017 12:48:19 %S A291887 1,3,11,31,91,250,690,1863,5017,13389,35621,94354,249352,657421, %T A291887 1730685,4550031,11950963,31365810,82274126,215711947,565376593, %U A291887 1481448697,3881041065,10165822434,26624745964,69725071281,182583838181,478093234315,1251829592839 %N A291887 Number of symmetrically unique Dyck paths of semilength n and height three. %H A291887 Alois P. Heinz, <a href="/A291887/b291887.txt">Table of n, a(n) for n = 3..1000</a> %H A291887 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (6, -9, -8, 27, -10, -10, 4). %F A291887 G.f.: -x^3*(x^4+2*x^2-3*x+1)/((2*x-1)*(x^2-3*x+1)*(2*x^2-1)*(x^2+x-1)). %Y A291887 Column k=3 of A291883. %K A291887 nonn,easy %O A291887 3,2 %A A291887 _Alois P. Heinz_, Sep 05 2017