%I #10 May 09 2021 19:00:50
%S 1,1,1,2,7,18,68,251,1020,4258,18580,82716,377207,1748250,8227066,
%T 39197164,188824506,918333933,4504366940,22260929867,110763984273,
%U 554510459987,2791460440109,14123739733754,71792405634223,366483503897357,1878163540497162,9660232634407657
%N Number of unlabeled oriented edgerooted 2trees which have n triangles.
%H Andrew Howroyd, <a href="/A303742/b303742.txt">Table of n, a(n) for n = 0..500</a>
%H T. Fowler, I. Gessel, G. Labelle, P. Leroux, <a href="https://doi.org/10.1006/aama.2001.0771">The specification of 2trees</a>, Adv. Appl. Math. 28 (2) (2002) 145168, Table 1.
%o (PARI) C(30,3) \\ See A340812 for C(n,k).  _Andrew Howroyd_, May 09 2021
%Y Column k=3 of A340812.
%K nonn
%O 0,4
%A _R. J. Mathar_, Apr 29 2018
%E Name clarified by _Andrew Howroyd_, May 09 2021
