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A303742 Oriented edge-rooted 2-trees which have n labeled triangles. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..27.

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

CROSSREFS

Sequence in context: A000988 A185308 A002214 * A218684 A100408 A259370

Adjacent sequences:  A303739 A303740 A303741 * A303743 A303744 A303745

KEYWORD

nonn

AUTHOR

R. J. Mathar, Apr 29 2018

STATUS

approved

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Last modified February 15 16:53 EST 2019. Contains 320136 sequences. (Running on oeis4.)