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A000421 Number of isomorphism classes of connected 3-regular loopless multigraphs of order 2n. 11
1, 2, 6, 20, 91, 509, 3608, 31856, 340416, 4269971, 61133757, 978098997 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) is also the number of isomorphism classes of connected 3-regular simple graphs of order 2n with possibly loops. - Nico Van Cleemput, Jun 04 2014

REFERENCES

A. T. Balaban, Enumeration of Cyclic Graphs, pp. 63-105 of A. T. Balaban, ed., Chemical Applications of Graph Theory, Ac. Press, 1976; see p. 92.

CRC Handbook of Combinatorial Designs, 1996, p. 651.

Brendan McKay, software at http://users.cecs.anu.edu.au/~bdm/nauty/

LINKS

Table of n, a(n) for n=1..12.

G. Brinkmann, N. Van Cleemput, T.Pisanski, Generation of various classes of trivalent graphs, Theoretical Computer Science 502, 2013, pp.16-29.

PROG

(nauty/bash) for n in {1..10}; do geng -cqD3 $[2*$n] | multig -ur3; done # Sean A. Irvine, Sep 24 2015

CROSSREFS

Cf. A129416, A005967, A129417, A129419, A129421, A129423, A129425

Sequence in context: A027321 A027315 A005965 * A009244 A104985 A210690

Adjacent sequences:  A000418 A000419 A000420 * A000422 A000423 A000424

KEYWORD

nonn,hard,more

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Brendan McKay, Apr 15 2007

STATUS

approved

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Last modified June 22 08:08 EDT 2017. Contains 288605 sequences.