A112923 Number of nonisomorphic connected bipartite Y-graphs Y(n:i,j,k) on 8n vertices (or nodes) for 1<=i,j,k<=n.

1, 1, 2, 2, 5, 4, 5, 7, 9, 7, 14, 10, 15, 23, 15, 15, 27, 19, 28, 39, 29, 26, 45, 36, 39

Offset

2,3

Comments

A Y-graph Y(n:i,j,k) has 4n vertices arranged in four segments of n vertices. Let the vertices be v_{x,y} for x=0,1,2,3 and y in the integers modulo n. The edges are v_{1,y}v_{1,y+i}, v_{2,y}v_{2,y+j}, v_{2,y}v_{2,y+k} and v_{0,y}v_{x,y}, where y=0,1,...,n-1 and x=1,2,3 and the subscript addition is performed modulo n.

References

I. Z. Bouwer, W. W. Chernoff, B. Monson, and Z. Starr (Editors), "Foster's Census", Charles Babbage Research Centre, Winnipeg, 1988.

Links

Table of n, a(n) for n=2..26.

J. D. Horton and I. Z. Bouwer, Symmetric Y-graphs and H-graphs, J. Comb. Theory B 53 (1991) 114-129.

Example

Y(4:1,1,1) is the smallest bipartite Y-graph.
Y(14:1,3,5) is the smallest bipartite symmetric (vertex- and edge-transitive) Y-graph.

Crossrefs

Cf. A112921, A112922, A112924.

Sequence in context: A206427 A335690 A330026 * A337662 A286099 A098366

Adjacent sequences: A112920 A112921 A112922 * A112924 A112925 A112926

Keyword

nonn,more

Author

Marko Boben (Marko.Boben(AT)fmf.uni-lj.si), Tomaz Pisanski and Arjana Zitnik (Arjana.Zitnik(AT)fmf.uni-lj.si), Oct 06 2005

Status

approved