A006648 Number of graphs with n nodes, n-1 edges and no isolated vertices. (Formerly M1181)

1, 1, 2, 4, 9, 20, 50, 124, 332, 895, 2513, 7172, 20994, 62366, 188696, 578717, 1799999, 5666257, 18047319, 58097540, 188953756, 620493315, 2056582095, 6877206111, 23195975865, 78891742748, 270505303760, 934890953041, 3256230606767

Offset

2,3

References

W. L. Kocay, Some new methods in reconstruction theory, pp. 89 - 114 of Combinatorial Mathematics IX. Proc. Ninth Australian Conference (Brisbane, August 1981). Ed. E. J. Billington, S. Oates-Williams and A. P. Street. Lecture Notes Math., 952. Springer-Verlag, 1982.

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=2..30.

Formula

a(n) = A001433(n) - A001434(n - 1). - Sean A. Irvine, Jun 06 2017

Crossrefs

Cf. A001433, A001434.

Sequence in context: A093637 A068051 A032289 * A128496 A134955 A171887

Adjacent sequences: A006645 A006646 A006647 * A006649 A006650 A006651

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

More terms from Vladeta Jovovic, Mar 02 2008

More terms from Sean A. Irvine, Jun 06 2017

Status

approved