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 A071726 #6 May 30 2020 17:32:23
%S A071726 1,1,2,6,16,47,146,471,1562,5291,18226,63648,224808,801686,2882452,
%T A071726 10437745,38032110,139339635,512996370,1896907980,7041759120,
%U A071726 26233530210,98046684060,367525880670,1381386710964,5205006015102
%N A071726 Expansion of (1+x^3*C)*C, where C = (1-(1-4*x)^(1/2))/(2*x) is g.f. for Catalan numbers, A000108.
%H A071726 Michael De Vlieger, <a href="/A071726/b071726.txt">Table of n, a(n) for n = 0..1000</a>
%H A071726 Stoyan Dimitrov, <a href="https://arxiv.org/abs/2002.12322">On permutation patterns with constrained gap sizes</a>, arXiv:2002.12322 [math.CO], 2020.
%t A071726 With[{$MaxExtraPrecision = 1000}, CoefficientList[Series[# (1 + x^3*#) &[(1 - (1 - 4 x)^(1/2))/(2 x)], {x, 0, 25}], x]] (* _Michael De Vlieger_, May 30 2020 *)
%K A071726 nonn
%O A071726 0,3
%A A071726 _N. J. A. Sloane_, Jun 06 2002