Glasnik Matematicki, Vol. 34, No.2 (1999), 109-121.

SYMMETRIC (70,24,8) DESIGNS HAVING Frob21 × Z2 AS AN AUTOMORPHISM GROUP

Dean Crnković

Department of Mathematics, Faculty of Philosophy in Rijeka, Omladinska 14, 51000 Rijeka, Croatia
e-mail: deanc@mapef.pefri.hr

Abstract.   Up to isomorphism there are twenty-two symmetric (70,24,8) designs having automorphism group isomorphic to Frob21 × Z2. Among them there are four self-dual, and nine pairs of dual designs. Full automorphism groups of those designs are isomorphic to Frob21 × Z2. Designs are constructed by means of tactical decompositions, using a principal series of the group Frob21 × Z2.

1991 Mathematics Subject Classification.   05B05.

Key words and phrases.   Symmetric design, automorphism group, orbit structure.

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