The sub-class sizes of some elements being square free

Let [Formula: see text] be an element of a finite group [Formula: see text], and [Formula: see text] a prime factor of the order of [Formula: see text]. It is clear that there always exists a unique minimal subnormal subgroup containing [Formula: see text], say [Formula: see text]. We call the conjugacy class of [Formula: see text] in [Formula: see text] the sub-class of [Formula: see text] in [Formula: see text], see [G. Qian and Y. Yang, On sub-class sizes of finite groups, J. Aust. Math. Soc. (2020) 402–411]. In this paper, assume that [Formula: see text] is the product of the subgroups [Formula: see text] and [Formula: see text], we investigate the solvability, [Formula: see text]-nilpotence and supersolvability of the group [Formula: see text] under the condition that the sub-class sizes of prime power order elements in [Formula: see text] are [Formula: see text] free, [Formula: see text] free and square free, respectively, so that some known results relevant to conjugacy class sizes are generalized.

Several Results on Conjugacy Class Sizes of Some Elements of Finite Groups

Let G be a finite group. For an element x of G, xG denotes the conjugacy class of x in G. |xG| is called the size of the conjugacy class xG. In this paper, we establish several results on conjugacy class sizes of some elements of finite groups. In addition, we give a simple and clearer proof of a known result.

On characterization of a finite group by the set of conjugacy class sizes

Let [Formula: see text] be a finite group and [Formula: see text] be the set of its conjugacy class sizes. In the 1980s, Thompson conjectured that the equality [Formula: see text], where [Formula: see text] and [Formula: see text] is simple, implies the isomorphism [Formula: see text]. In a series of papers of different authors, Thompson’s conjecture was proved. In this paper, we show that in some cases it is possible to omit the conditions [Formula: see text] and [Formula: see text] is simple and prove a more general result.

A note on class sizes of vanishing elements in finite groups

Let [Formula: see text] and [Formula: see text] be normal subgroups of a finite group [Formula: see text]. We obtain th supersolvability of a factorized group [Formula: see text], given that the conjugacy class sizes of vanishing elements of prime-power order in [Formula: see text] and [Formula: see text] are square-free.

Conjugacy class sizes in arithmetic progression

Let {\mathrm{cs}(G)} denote the set of conjugacy class sizes of a group G, and let \mathrm{cs}^{*}(G)=\mathrm{cs}(G)\setminus\{1\} be the sizes of non-central classes. We prove three results. We classify all finite groups for which (1) {\mathrm{cs}(G)=\{a,a+d,\dots,a+rd\}} is an arithmetic progression with {r\geqslant 2}; (2) {\mathrm{cs}^{*}(G)=\{2,4,6\}} is the smallest case where {\mathrm{cs}^{*}(G)} is an arithmetic progression of length more than 2 (our most substantial result); (3) the largest two members of {\mathrm{cs}^{*}(G)} are coprime. For (3), it is not obvious, but it is true that {\mathrm{cs}^{*}(G)} has two elements, and so is an arithmetic progression.

On solvable groups with one vanishing class size

Let G be a finite group, and let cs(G) be the set of conjugacy class sizes of G. Recalling that an element g of G is called a vanishing element if there exists an irreducible character of G taking the value 0 on g, we consider one particular subset of cs(G), namely, the set vcs(G) whose elements are the conjugacy class sizes of the vanishing elements of G. Motivated by the results inBianchi et al. (2020, J. Group Theory, 23, 79–83), we describe the class of the finite groups G such that vcs(G) consists of a single element under the assumption that G is supersolvable or G has a normal Sylow 2-subgroup (in particular, groups of odd order are covered). As a particular case, we also get a characterization of finite groups having a single vanishing conjugacy class size which is either a prime power or square-free.