Original scientific paper
Classification of symmetric block design for (71,21,6) with nonabelian group of order 21
E. Ademaj
M. Essert
Abstract
The existence of symmetric block designs for (71,21,6) was
doubtful until the discovery of Z. Janko and T. van Trung of the
so-called "non-human" design [3]. In this paper we have classified
designs with the above parameters, admitting all possible actions
of the nonabelian group of order 21 on them, which is indeed the
full automorphism group of the Janko-van Trung design. We have
proved that there is only one symmetric block design for (71,21,6), together with its dual, with the Frobenius group of order 21, namely the Janko-van Trung design.
Keywords
block design; automorphism group; collineation
Hrčak ID:
714
URI
Publication date:
26.6.2004.
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