%I A112917
%S A112917 1,1,4,6,7,13,19,31,24,76,41,77,116,116,87,226,115,307,276,308,201,671,
%T A112917 317,523,478,786,403,1495
%N A112917 Number of nonisomorphic H-graphs H(n:i,j;k,m) on 6n vertices (or nodes) 
               for 1<=i,j,k,m<n/2.
%C A112917 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.
%D A112917 I. Z. Bouwer, W. W. Chernoff, B. Monson and Z. Starr (Eds.), "Foster's 
               Census", Charles Babbage Research Centre, Winnipeg, 1988.
%D A112917 J. D. Horton and I. Z. Bouwer, Symmetric Y-graphs and H-graphs, J. Comb. 
               Theory B 53 (1991) 114-129
%e A112917 The only connected symmetric H-graphs are H(17:1,4;2,8) and H(34:1,13;
               9,15) which are also listed in Foster's Census.
%Y A112917 Cf. A112918, A112919, A112920, A112921, A107452.
%Y A112917 Sequence in context: A102138 A002151 A054063 this_sequence A102141 A107919 
               A165404
%Y A112917 Adjacent sequences: A112914 A112915 A112916 this_sequence A112918 A112919 
               A112920
%K A112917 nonn
%O A112917 3,3
%A A112917 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