Some new symmetric designs with parameters (64,28,12) Original Research Article

Fortysix mutually nonisomorphic symmetric (64,28,12)-designs have been constructed by means of tactical decompositions. They all admit an action of the nonabelian group of order 21. The computation of their full automorphism groups as well as their derived (28,12,11)-designs proves that none of them can be isomorphic to any of the known (64,28,12)-designs.