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A063687 Number of 2-trees rooted at any symmetric edge. 2
1, 1, 1, 2, 3, 6, 10, 21, 38, 84, 156, 352, 677, 1562, 3054, 7148, 14196, 33603, 67474, 161121, 326519, 785305, 1603111, 3878194, 7965845, 19365811, 39983300, 97610247, 202424674, 495955345, 1032460679, 2537529717, 5300256499 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

REFERENCES

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 75, Eq. (3.5.9).

LINKS

Table of n, a(n) for n=0..32.

CROSSREFS

Cf. A058870, A058866, A054581.

Sequence in context: A008928 A124343 A032291 * A002988 A138347 A211180

Adjacent sequences:  A063684 A063685 A063686 * A063688 A063689 A063690

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Aug 22 2001

STATUS

approved

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Last modified November 16 00:11 EST 2018. Contains 317252 sequences. (Running on oeis4.)