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 A112921 Number of nonisomorphic Y-graphs Y(n:i,j,k) on 4n vertices (or nodes) for 1<=i,j,k
 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 (list; graph; refs; listen; history; text; internal format)
 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 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: A023847 A000061 A153176 * A215205 A210948 A008133 Adjacent sequences:  A112918 A112919 A112920 * A112922 A112923 A112924 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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