A058866 Number of 2-trees rooted at an edge.

1, 2, 6, 21, 83, 356, 1599, 7434, 35381, 171508, 843419, 4197179, 21094355, 106915928, 545859112, 2804656069, 14491370996, 75248398034, 392476363133, 2055245992376, 10801442696736, 56953957110855, 301207378815752

Offset: 1

Author

N. J. A. Sloane, Jan 06 2001

Keywords

• nonn
• easy

References

• F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 75, Eq. (3.5.11).

Crossrefs

Let A063687(n) be the number of 2-trees rooted at a symmetric edge (see H. and P. Eq. (3.5.9)). Then A058866(n) = A058870(n) + A063687(n).

Cf. A058870, A054581.

Formula

H. and P. give g.f.

Extensions

More terms from Vladeta Jovovic, Aug 22 2001