
COMMENTS

Definition (2): Number of Eulerian 2multigraphs with n nodes.
Definition (3): Number of switching classes of signed graphs on n unlabeled nodes.
Definition (4): Number of switching classes of 2multigraphs with n nodes
Definition (1) is same as Definition (2).  Vladeta Jovovic, Mar 15 2009
Definition (3) is same as Definition (4).  Vladeta Jovovic, Mar 15 2009
That Definition (2) is same as Definition (4) follows from Theorem 8.3 of Cameron (1977).  N. J. A. Sloane, Mar 22 2009


REFERENCES

Bussemaker, F. C.; Cameron, P. J.; Seidel, J. J.; and Tsaranov, S. V., Tables of signed graphs, ReportWSK 9101, Eindhoven University of Technology, Department of Mathematics and Computing Science, Eindhoven, 1991, 105 pp. MR: 92g:05001.
P. J. Cameron, Cohomological aspects of twographs, Math. Zeit., 157 (1977), 101119.
R. W. Robinson, personal communication.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1980.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


EXTENSIONS

Extended by N. J. A. Sloane from Robinson's table, Oct 20 2006
Edited by N. J. A. Sloane, Mar 30 2009. Does the Cameron paper provide a formula? What about the labeled version? (Compare A002854.)
Corrected by Vladeta Jovovic, Apr 04 2009
