1,2

Definition (2): Number of Eulerian 2-multigraphs with n nodes.

Definition (3): Number of switching classes of signed graphs on n unlabeled nodes.

Definition (4): Number of switching classes of 2-multigraphs with n nodes

Definition (1) is same as Definition (2). - Vladeta Jovovic, March 15 2009

Definition (3) is same as Definition (4). - Vladeta Jovovic, March 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

Bussemaker, F. C.; Cameron, P. J.; Seidel, J. J.; and Tsaranov, S. V., Tables of signed graphs, Report-WSK 91-01, Eindhoven University of Technology, Department of Mathematics and Computing Science, Eindhoven, 1991, 105 pp. MR: 92g:05001.

P. J. Cameron, Cohomological aspects of two-graphs, Math. Zeit., 157 (1977), 101-119.

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).

Cf. A002854, A084565, A004102.

Sequence in context: A123310 A058119 A075634 this_sequence A005639 A093730 A007769

Adjacent sequences: A007124 A007125 A007126 this_sequence A007128 A007129 A007130

nonn,nice

N. J. A. Sloane (njas(AT)research.att.com).

Extended by N. J. A. Sloane (njas(AT)research.att.com) 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 (vladeta(AT)eunet.yu), Apr 04 2009