This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A007127 M1517 #25 Mar 02 2021 04:53:00 %S A007127 1,2,5,18,100,1242,43425,4925635,1678993887,1613875721946, %T A007127 4293014800909806,31574944534364259507,644483327087699659771857, %U A007127 36676558984788056550610362834,5846161177591490590945591554686844,2621219060849255874034814155021919844156 %N A007127 Definition (1): Number of unlabeled strength-2 Eulerian graphs with n nodes. %C A007127 Definition (2): Number of Eulerian 2-multigraphs with n nodes. %C A007127 Definition (3): Number of switching classes of signed graphs on n unlabeled nodes. %C A007127 Definition (4): Number of switching classes of 2-multigraphs with n nodes %C A007127 Definition (1) is same as Definition (2). - Vladeta Jovovic, Mar 15 2009 %C A007127 Definition (3) is same as Definition (4). - Vladeta Jovovic, Mar 15 2009 %C A007127 That Definition (2) is same as Definition (4) follows from Theorem 8.3 of Cameron (1977). - _N. J. A. Sloane_, Mar 22 2009 %D A007127 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). %D A007127 R. W. Robinson, personal communication. %D A007127 R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1980. %D A007127 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A007127 F. C. Bussemaker, P. J. Cameron, J. J. Seidel, and S. V. Tsaranov, <a href="https://www.researchgate.net/publication/241872284_Tables_of_signed_graphs ">Tables of signed graphs</a>, Report-WSK 91-01, Eindhoven University of Technology, Department of Mathematics and Computing Science, Eindhoven, 1991, 105 pp. (MR: 92g:05001). %H A007127 P. J. Cameron, <a href="https://doi.org/10.1007/BF01215145">Cohomological aspects of two-graphs</a>, Math. Zeit., 157 (1977), 101-119. %Y A007127 Cf. A002854, A084565, A004102. %K A007127 nonn,nice %O A007127 1,2 %A A007127 _N. J. A. Sloane_ %E A007127 Extended by _N. J. A. Sloane_ from Robinson's table, Oct 20 2006 %E A007127 Edited by _N. J. A. Sloane_, Mar 30 2009. Does the Cameron paper provide a formula? What about the labeled version? (Compare A002854.) %E A007127 Corrected by _Vladeta Jovovic_, Apr 04 2009