[1] Budapest Univ Technol & Econ, Inst Math, Dept Algebra, Muegyet Rkp 3, H-1111 Budapest, Hungary
[2] Budapest Univ Technol & Econ, Inst Math, Dept Stochast, Muegyet Rkp 3, H-1111 Budapest, Hungary
[3] Budapest Univ Technol & Econ, Dept Comp Sci & Informat Theory, Muegyet Rkp 3, H-1111 Budapest, Hungary
[4] ELKH, MTA BME Lendulet Arithmet Combinator Res Grp, Muegyet Rkp 3, H-1111 Budapest, Hungary