This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A133279 Number of unlabeled mating graphs with n nodes and a degenerate adjacency matrix. 0
 1, 0, 1, 1, 7, 21, 234, 2252, 64420, 2148355, 183956671 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS Mating graphs are graphs where no two nodes have the same set of neighbors. Graphs with an invertible adjacency matrix are mating graphs. LINKS FORMULA a(n) = A004110(n) - A109717(n). MATHEMATICA k = {}; For[i = 1, i < 8, i++, lg = ListGraphs[i] ; len = Length[lg]; k = Append[k, Length[Select[Range[len], Det[ToAdjacencyMatrix[lg[[ # ]]]] == 0 && Length[Union[ToAdjacencyMatrix[lg[[ # ]]]]] == i &]]]]; k CROSSREFS Cf. A004110, A109717. Sequence in context: A183938 A060146 A111878 * A192734 A220161 A213152 Adjacent sequences:  A133276 A133277 A133278 * A133280 A133281 A133282 KEYWORD nonn,more AUTHOR Tanya Khovanova, Aug 27 2008 EXTENSIONS a(8)-a(11) by Shreeyash Gotmare, Aug 28 2017 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 January 18 23:05 EST 2019. Contains 319282 sequences. (Running on oeis4.)