The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A126750 Number of 2-connected (or biconnected) graphs on n nodes with chromatic number 2. 1
 0, 0, 0, 1, 1, 5, 8, 42, 146, 956, 6643, 65921, 818448, 13442572, 287665498, 8099980771, 300760170216, 14791653463768, 967055338887805, 84368806391412395, 9855854129239183783, 1546801291978378704267 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS Equally, number of 2-connected (or biconnected) bipartite graphs on n nodes. Also number of biconnected triangle-free graphs on n nodes with chromatic number 2, since chromatic number 2 implies triangle-free. - Gordon Royle, Apr 11 2007 See the Gainer-Dewar/Gessel reference for formulas and Sage code. - Ralf Stephan, May 18 2013 LINKS Keith M. Briggs, Combinatorial Graph Theory C. J. Colbourn and C. Huybrechts, Fully gated graphs,: recognition and convex operations, Discrete Math., 308 (2008), 5184-5195. A. Gainer-Dewar and I. M. Gessel, Enumeration of bipartite graphs and bipartite blocks, arXiv:1304.0139 [math.CO], 2013-2014. CROSSREFS A diagonal of triangle in A126749. Sequence in context: A192272 A073930 A130223 * A256401 A109292 A275571 Adjacent sequences:  A126747 A126748 A126749 * A126751 A126752 A126753 KEYWORD nonn AUTHOR N. J. A. Sloane, Feb 18 2007, Oct 01 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 1 04:57 EDT 2020. Contains 334758 sequences. (Running on oeis4.)