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

1,3

REFERENCES

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

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

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

LINKS

Table of n, a(n) for n=1..17.

E. M. Palmer and R. C. Read, On the number of plane 2-trees, J. Lond. Math. Soc., 6 (1973), 583-592. [Annotated and corrected scanned copy]

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

Sequence in context: A210899 A302903 A259467 * A187535 A263421 A046673

Adjacent sequences:  A003089 A003090 A003091 * A003093 A003094 A003095

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified November 17 19:15 EST 2018. Contains 317276 sequences. (Running on oeis4.)