A063687 Number of 2-trees rooted at any symmetric edge.

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

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: A124343 A324407 A032291 * A359019 A002988 A138347

Adjacent sequences: A063684 A063685 A063686 * A063688 A063689 A063690

Keyword

nonn

Author

Vladeta Jovovic, Aug 22 2001

Status

approved