

A078792


Number of unlabeled 3trees on n vertices.


4



0, 0, 1, 1, 1, 2, 5, 15, 58, 275, 1505, 9003, 56931, 372973, 2506312, 17165954, 119398333, 841244274, 5993093551, 43109340222, 312747109787, 2286190318744, 16826338257708, 124605344758149, 927910207739261, 6945172081954449, 52225283886702922
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OFFSET

1,6


COMMENTS

A ktree is recursively defined as follows: K_k is a ktree and any ktree on n+1 vertices is obtained by joining a new vertex to a kclique in a ktree on n vertices.


REFERENCES

Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, page 328.


LINKS

Table of n, a(n) for n=1..27.
Andrew GainerDewar, GammaSpecies and the Enumeration of kTrees, Electronic Journal of Combinatorics, Volume 19 (2012), #P45.  From N. J. A. Sloane, Dec 15 2012


CROSSREFS

Cf. A036362 (labeled 3trees), A054581 (unlabeled 2trees).
Sequence in context: A334155 A348365 A048192 * A208808 A266682 A325575
Adjacent sequences: A078789 A078790 A078791 * A078793 A078794 A078795


KEYWORD

nonn


AUTHOR

Gordon F. Royle, Dec 05 2002


EXTENSIONS

More terms from Andrew R. Gainer, Dec 03 2011


STATUS

approved



