A112921 Number of nonisomorphic Y-graphs Y(n:i,j,k) on 4n vertices (or nodes) for 1<=i,j,k<n/2.

1, 1, 2, 4, 4, 6, 8, 10, 7, 24, 10, 20, 26, 26, 15, 44, 19, 54, 44, 44, 26, 102, 38, 62, 57, 96, 40, 164, 46, 104, 91, 102, 91, 213, 64, 128, 124, 222, 77, 290, 85, 212, 200, 184, 100, 388, 128, 268, 199, 292, 126

Offset

3,3

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.

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

Links

Table of n, a(n) for n=3..53.

Example

Y(7:1,2,3) is the Coxeter graph, the only (connected) symmetric (vertex- and edge-transitive) Y-graph of girth 7 or less.

Crossrefs

Cf. A112922, A112923, A112924, A112921, A107452.

Sequence in context: A153176 A229144 A263021 * A339905 A215205 A298043

Adjacent sequences: A112918 A112919 A112920 * A112922 A112923 A112924

Keyword

nonn

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