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A058866 Number of 2-trees rooted at a edge. 8
1, 2, 6, 21, 83, 356, 1599, 7434, 35381, 171508, 843419, 4197179, 21094355, 106915928, 545859112, 2804656069, 14491370996, 75248398034, 392476363133, 2055245992376, 10801442696736, 56953957110855, 301207378815752 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

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

LINKS

Table of n, a(n) for n=1..23.

FORMULA

H. and P. give g.f.

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, A058870, A054581.

Sequence in context: A148495 A150221 A063689 * A178325 A087649 A150222

Adjacent sequences:  A058863 A058864 A058865 * A058867 A058868 A058869

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Jan 06 2001

EXTENSIONS

More terms from Vladeta Jovovic, Aug 22 2001

STATUS

approved

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Last modified November 13 11:09 EST 2018. Contains 317133 sequences. (Running on oeis4.)