OFFSET
1,3
COMMENTS
A mating-type graph has all different rows in its adjacency matrix.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..50
Ronald C. Read, The enumeration of mating-type graphs, Report CORR 89-38, Dept. Combinatorics and Optimization, Univ. Waterloo, 1989.
Gus Wiseman, The a(4) = 32 non-mating-type graphs.
FORMULA
MATHEMATICA
Table[Length[Select[Subsets[Subsets[Range[n], {2}]], !UnsameQ@@AdjacencyMatrix[Graph[Range[n], #]]&]], {n, 5}]
PROG
(PARI) a(n) = {2^binomial(n, 2) - sum(k=0, n, stirling(n, k, 1)*2^binomial(k, 2))} \\ Andrew Howroyd, Sep 11 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 05 2019
EXTENSIONS
Terms a(7) and beyond from Andrew Howroyd, Sep 11 2019
STATUS
approved