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A007127
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Definition (1): Number of unlabeled strength-2 Eulerian graphs with n nodes.
(Formerly M1517)
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2
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1, 2, 5, 18, 100, 1242, 43425, 4925635, 1678993887, 1613875721946, 4293014800909806, 31574944534364259507, 644483327087699659771857, 36676558984788056550610362834, 5846161177591490590945591554686844, 2621219060849255874034814155021919844156
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OFFSET
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1,2
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COMMENTS
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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
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REFERENCES
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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).
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LINKS
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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).
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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Edited by N. J. A. Sloane, Mar 30 2009. Does the Cameron paper provide a formula? What about the labeled version? (Compare A002854.)
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STATUS
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approved
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