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 A112917 Number of nonisomorphic H-graphs H(n:i,j;k,m) on 6n vertices (or nodes) for 1<=i,j,k,m
 1, 1, 4, 6, 7, 13, 19, 31, 24, 76, 41, 77, 116, 116, 87, 226, 115, 307, 276, 308, 201, 671, 317, 523, 478, 786, 403, 1495 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,3 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. LINKS Table of n, a(n) for n=3..30. J. D. Horton and I. Z. Bouwer, Symmetric Y-graphs and H-graphs, J. Comb. Theory B 53 (1991) 114-129. EXAMPLE 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. CROSSREFS Cf. A112918, A112919, A112920, A112921, A107452. Sequence in context: A192046 A286488 A054063 * A102141 A107919 A165404 Adjacent sequences: A112914 A112915 A112916 * A112918 A112919 A112920 KEYWORD nonn,more 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

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Last modified September 11 21:10 EDT 2024. Contains 375839 sequences. (Running on oeis4.)