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 A133181 Number of distinct connected simple symmetric (edge- and vertex-transitive) graphs with n nodes. 3
 1, 1, 1, 2, 2, 4, 2, 5, 4, 8, 2, 11, 4, 8, 10 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Care is needed with "symmetric" terminology, which is variously used to mean both arc-transitive and both vertex- and edge-transitive. The symmetry means that any two vertices and any two edges are equivalent. In other words, if we have an initial labeling of the graph with vertices A and B adjacent (directly connected by an edge), we can relabel any two adjacent vertices as A and B and then relabel the remaining vertices so that new graph will be equal to the initial. The first known difference from A286280 (connected arc-transitive graphs on n vertices) occurs at a(27), corresponding to the Doyle graph (which is both edge- and vertex-transitive but not arc-transitive). - Eric W. Weisstein, May 13 2017 By convention, empty graphs are considered edge-transitive (and hence symmetric). LINKS Eric Weisstein's World of Mathematics, Arc-Transitive Graph Eric Weisstein's World of Mathematics, Doyle Graph Eric Weisstein's World of Mathematics, Edge-Transitive Graph Eric Weisstein's World of Mathematics, Symmetric Graph Eric Weisstein's World of Mathematics, Vertex-Transitive Graph EXAMPLE The complete graph is symmetrical. In addition, if the number of vertices is > 3, the simple cycle through all vertices is symmetrical. Graphs determined by vertices and edges of Platonic solids are symmetrical. The square K X K grid with right vertices connected to corresponding left vertices and bottom vertices connected to corresponding top vertices is symmetrical. The smallest nontrivial and non-Platonic symmetric graph is the hexagon with connected opposite vertices. An example of symmetrical graph with 13 vertices: 0 connected to 1, 2, 3, 4 1 connected to 0, 5, 6, 7 2 connected to 0, 5, 8, 9 3 connected to 0, 6, 10, 11 4 connected to 0, 8, 10, 12 5 connected to 1, 2, 10, 11 6 connected to 1, 3, 8, 12 7 connected to 1, 8, 9, 11 8 connected to 2, 4, 6, 7 9 connected to 2, 7, 10, 12 10 connected to 3, 4, 5, 9 11 connected to 3, 5, 7, 12 12 connected to 4, 6, 9, 11 CROSSREFS Cf. A087145 (number of disconnected simple symmetric graphs on n nodes). Cf. A286931 (number of not necessarily connected simple symmetrical graphs with n nodes). Cf. A286280 (number of connected arc-transitive graphs of order n). Sequence in context: A139555 A241814 A088371 * A286280 A290088 A179013 Adjacent sequences:  A133178 A133179 A133180 * A133182 A133183 A133184 KEYWORD hard,nice,nonn AUTHOR Eugene Vasilchenko (eugene(AT)vasilchenko.net), Oct 10 2007, Oct 14 2007 EXTENSIONS a(1) and a(2) changed from 0 to 1 (since K_1 and K_2 are connected, vertex-transitive, and edge-transitive) by Eric W. Weisstein, May 16 2017 STATUS approved

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Last modified April 24 22:18 EDT 2019. Contains 322446 sequences. (Running on oeis4.)