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

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

Author

N. J. A. Sloane

Keywords

• nonn

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).

Crossrefs

Cf. A001433, A001434.

Formula

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

Extensions

More terms from Vladeta Jovovic, Mar 02 2008

More terms from Sean A. Irvine, Jun 06 2017