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A003092
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Number of labeled plane 2-trees with n nodes.
(Formerly M2159)
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0
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0, 1, 2, 36, 1200, 57000, 3477600, 257826240, 22438563840, 2238543216000, 251584613280000, 31431367287936000, 4319334744012288000, 647313578549730892800, 105041172967733882880000, 18345770194541665075200000, 3430869798262479024291840000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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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).
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LINKS
| Index entries for sequences related to trees
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FORMULA
| n(n-1)^2 (5n-10)!/(4n-6)!.
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MAPLE
| [ seq(n*(n-1)^2*(5*n-10)!/(4*n-6)!, n=2..20) ];
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CROSSREFS
| Sequence in context: A166473 A009539 A009554 * A187535 A046673 A174580
Adjacent sequences: A003089 A003090 A003091 * A003093 A003094 A003095
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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