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A003093 Number of planar 2-trees with n nodes.
(Formerly M1977)
3
1, 2, 10, 83, 690, 6412, 61842, 617025, 6302725, 65619820, 693643860, 7425181257, 80326705270, 876832043840, 9645743783040, 106827450870525, 1190150414448795, 13329010510209790, 149976822229984908, 1694617702395672670, 19220402733369657820 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,2

COMMENTS

Table 2 of Palmer and Read paper gives incorrect value a(10) = 457025. - Sean A. Irvine, Feb 12 2016

REFERENCES

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=3..23.

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

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

G.f.: P(x) + (1/2) * x^2 * ((1 - T(x^2))^(-1) - 1) + (2/3) * x^3 * (1 - T(x^3))^(-2) where P(x) = Sum((k * (k - 1) * (5*k-10)! / (4*k-6)!) * x^k / k!) is the e.g.f. of A003092 and T(x) = Sum(((5 * k - 2)!/ (4 * k - 1)!) * x^k / k!) is the e.g.f. of A120348. - Sean A. Irvine, Feb 12 2016

CROSSREFS

Sequence in context: A281547 A111265 A296667 * A006679 A050390 A298690

Adjacent sequences:  A003090 A003091 A003092 * A003094 A003095 A003096

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

a(10) corrected and more terms from Sean A. Irvine, Feb 12 2016

STATUS

approved

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Last modified April 24 00:02 EDT 2019. Contains 322404 sequences. (Running on oeis4.)