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 A303742 #10 May 09 2021 19:00:50 %S A303742 1,1,1,2,7,18,68,251,1020,4258,18580,82716,377207,1748250,8227066, %T A303742 39197164,188824506,918333933,4504366940,22260929867,110763984273, %U A303742 554510459987,2791460440109,14123739733754,71792405634223,366483503897357,1878163540497162,9660232634407657 %N A303742 Number of unlabeled oriented edge-rooted 2-trees which have n triangles. %H A303742 Andrew Howroyd, <a href="/A303742/b303742.txt">Table of n, a(n) for n = 0..500</a> %H A303742 T. Fowler, I. Gessel, G. Labelle, P. Leroux, <a href="https://doi.org/10.1006/aama.2001.0771">The specification of 2-trees</a>, Adv. Appl. Math. 28 (2) (2002) 145-168, Table 1. %o A303742 (PARI) C(30,3) \\ See A340812 for C(n,k). - _Andrew Howroyd_, May 09 2021 %Y A303742 Column k=3 of A340812. %K A303742 nonn %O A303742 0,4 %A A303742 _R. J. Mathar_, Apr 29 2018 %E A303742 Name clarified by _Andrew Howroyd_, May 09 2021