Affiliation: | 1. Institute of Mathematics, University of Debrecen, Number Theory Research Group, Hungarian Academy of Sciences and University of Debrecen, H-4010 Debrecen, P.O. Box 12, Hungary;2. Institute of Informatics, University of Debrecen, H-4010 Debrecen, P.O. Box 12, Hungary;3. Institute of Mathematics, University of Natural Resources, Gregor Mendel Straße. 33, A-1180 Vienna, Austria |