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A003092 Number of labeled plane 2-trees with n nodes.
(Formerly M2159)
+0
1
0, 1, 2, 36, 1200, 57000, 3477600, 257826240, 22438563840, 2238543216000, 251584613280000, 31431367287936000, 4319334744012288000, 647313578549730892800, 105041172967733882880000, 18345770194541665075200000, 3430869798262479024291840000 (list; graph; listen)
OFFSET

1,3

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

E. M. Palmer and R. C. Read, on the number of plane 2-trees, J. Lond. Math. Soc., 6 (1973), 583-592.

F. Harary and E. Palmer, Graphical Enumeration, (1973), p. 30, Problem 1.14.

LINKS

Index entries for sequences related to trees

FORMULA

n(n-1)^2 (5n-10)!/(4n-6)!.

MAPLE

[ seq(n*(n-1)^2*(5*n-10)!/(4*n-6)!, n=2..20) ];

CROSSREFS

Adjacent sequences: A003089 A003090 A003091 this_sequence A003093 A003094 A003095

Sequence in context: A001626 A009539 A009554 this_sequence A046673 A088026 A126934

KEYWORD

nonn

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com).

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Last modified November 8 07:45 EST 2009. Contains 166143 sequences.


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