Abstract
The well-known Landau’s theorem states that, for any positive integer k, there are finitely many isomorphism classes of finite groups with exactly k (conjugacy) classes. We study variations of this theorem for p-regular classes as well as p-singular classes. We prove several results showing that the structure of a finite group is strongly restricted by the number of p-regular classes or the number of p-singular classes of the group. In particular, if G is a finite group with O p (G) = 1 then |G/F(G)| p' is bounded in terms of the number of p-regular classes of G. However, it is not possible to prove that there are finitely many groups with no nontrivial normal p-subgroup and k p-regular classes without solving some extremely difficult number-theoretic problems (for instance, we would need to show that the number of Fermat primes is finite).
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The research of the first author was supported by the Spanish Ministerio de Ciencia y Tecnología, grant MTM2010-15296 and PROMETEO/Generalitat Valenciana.
The second author is partially supported by the NSA Young Investigator Grant #H98230-14-1-0293 and a BCAS Faculty Scholarship Award from the Buchtel College of Arts and Sciences, The University of Akron.
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Moretó, A., Nguyen, H.N. Variations of Landau’s theorem for p-regular and p-singular conjugacy classes. Isr. J. Math. 212, 961–987 (2016). https://doi.org/10.1007/s11856-016-1316-7
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DOI: https://doi.org/10.1007/s11856-016-1316-7