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A112920 Number of nonisomorphic connected bipartite H-graphs H(n:i,j;k,m) with girth 6 on 6n vertices (or nodes) for 1<=i,j,k,m<n/2. 4
0, 0, 0, 1, 5, 3, 5, 3, 13, 8, 19, 27, 9, 19, 33, 74, 41, 19, 61, 75, 61, 137, 51, 108, 95, 111, 99, 217 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,5

COMMENTS

An H-graph H(n:i,j;k,m) has 6n vertices arranged in six segments of n vertices. Let the vertices be v_{x,y} for x=0,1,2,3,4,5 and y in the integers modulo n. The edges are v_{0,y}v_{1,y}, v_{0,y}v_{2,y}, v_{0,y}v_{3,y}, v_{1,y}v_{4,y}, v_{1,y}v_{5,y} (inner edges) and v_{2,y}v_{2,y+i}, v_{3,y}v_{3,y+j}, v_{4,y}v_{3,y+k}, v_{5,y}v_{5,y+m} (outer edges) where y=0,1,...,n-1 and 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..30.

EXAMPLE

The smallest H-graph with girth 6 is H(6:1,1;1,1).

CROSSREFS

Cf. A112917, A112919, A112920.

Sequence in context: A194624 A201762 A153386 * A109364 A122277 A198211

Adjacent sequences:  A112917 A112918 A112919 * A112921 A112922 A112923

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified May 19 22:35 EDT 2013. Contains 225436 sequences.