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A007127 Definition (1): Number of unlabeled strength-2 Eulerian graphs with n nodes.
(Formerly M1517)
2
1, 2, 5, 18, 100, 1242, 43425, 4925635, 1678993887, 1613875721946, 4293014800909806, 31574944534364259507, 644483327087699659771857, 36676558984788056550610362834, 5846161177591490590945591554686844, 2621219060849255874034814155021919844156 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
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, 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
F. C. Bussemaker, P. J. Cameron, J. J. Seidel, and S. V. Tsaranov, 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).
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).
LINKS
F. C. Bussemaker, P. J. Cameron, J. J. Seidel, and S. V. Tsaranov, 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.
CROSSREFS
Sequence in context: A333837 A075634 A322396 * A279207 A005639 A093730
KEYWORD
nonn,nice
AUTHOR
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
STATUS
approved

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Last modified March 28 04:55 EDT 2024. Contains 371235 sequences. (Running on oeis4.)