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%I #7 Oct 12 2013 15:12:49
%S 1,1,2,3,4,5,7,8,7,19,10,16,23,20,15,33,19,43,39,37,26,73,36,52,49,75,
%T 40,127,46,78,83,87,85,149,64,109,113,163,77,227,85,167,167,158,100,
%U 266,124,222,183,229,126
%N Number of nonisomorphic connected Y-graphs Y(n:i,j,k) on 4n vertices (or nodes) for 1<=i,j,k<n/2.
%C 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. It is connected if and only if gcd(n,i,j,k) = 1.
%D I. Z. Bouwer, W. W. Chernoff, B. Monson and Z. Starr (Editors), "Foster's Census", Charles Babbage Research Centre, Winnipeg, 1988.
%D J. D. Horton and I. Z. Bouwer, Symmetric Y-graphs and H-graphs, J. Comb. Theory B 53 (1991) 114-129
%e Y(7:1,2,3) is the Coxeter graph, the only symmetric (vertex- and edge-transitive) Y-graph of girth 7 or less.
%Y Cf. A112921, A112923, A112924.
%K nonn
%O 3,3
%A Marko Boben (Marko.Boben(AT)fmf.uni-lj.si), _Tomaz Pisanski_ and Arjana Zitnik (Arjana.Zitnik(AT)fmf.uni-lj.si), Oct 06 2005
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