A303742 Number of unlabeled oriented edge-rooted 2-trees which have n triangles.

1, 1, 1, 2, 7, 18, 68, 251, 1020, 4258, 18580, 82716, 377207, 1748250, 8227066, 39197164, 188824506, 918333933, 4504366940, 22260929867, 110763984273, 554510459987, 2791460440109, 14123739733754, 71792405634223, 366483503897357, 1878163540497162, 9660232634407657

Offset

0,4

Links

Andrew Howroyd, Table of n, a(n) for n = 0..500

T. Fowler, I. Gessel, G. Labelle, P. Leroux, The specification of 2-trees, Adv. Appl. Math. 28 (2) (2002) 145-168, Table 1.

Prog

(PARI) C(30, 3) \\ See A340812 for C(n, k). - Andrew Howroyd, May 09 2021

Crossrefs

Column k=3 of A340812.

Sequence in context: A000988 A185308 A002214 * A340738 A368593 A218684

Adjacent sequences: A303739 A303740 A303741 * A303743 A303744 A303745

Keyword

nonn

Author

R. J. Mathar, Apr 29 2018

Extensions

Name clarified by Andrew Howroyd, May 09 2021

Status

approved