A058668 Number of unlabeled graphs with n edges, no nodes of degree 1 and no cut nodes, under "series-equivalence"; multiple edges are allowed.

0, 1, 2, 5, 6, 13, 28

Offset

1,3

Comments

Under "series-equivalence" two graphs are equivalent if one can be obtained from the other by exchanging two subgraphs in series: replacing -A-B- by -B-A-.

Start with the graph consisting of a single edge together with the graphs described in A058642; apply the operations of replacing edges by two edges in series or parallel; discard equivalent graphs; the result is A058668.

References

B. D. H. Tellegen, Geometrical configurations and duality of electrical networks, Philips Technical Review, 5 (1940), 324-330.

Links

Table of n, a(n) for n=1..7.

Crossrefs

Cf. A058642.

Sequence in context: A247959 A243799 A029544 * A271640 A180744 A092790

Adjacent sequences: A058665 A058666 A058667 * A058669 A058670 A058671

Keyword

nonn,nice,more

Author

N. J. A. Sloane, Dec 30 2000

Status

approved