On finite groups with some subgroups of prime indices

We establish the solvability of each finite group whose every proper nonmaximal subgroup lies in some subgroup of prime index.     

On a class of relatively prime sequences

For each natural number n, let a₀(n) = n, and if a₀(n),…,a_i(n) have already been defined, let a_i+1(n) > a_i(n) be minimal with (a_i+1(n), a₀(n) … a_i(n)) = 1. Let g(n) be the largest a_i(n) not a prime or the square of a prime. We show that g(n) ～ n and that $\text{g(n) > n + cn}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{log}\text{(n)}$ for some c > 0. The true order of magnitude of g(n) ? n seems to be connected with the fine distribution of prime numbers. We also show that “most” a_i(n) that are not primes or squares of primes are products of two distinct primes. A result of independent interest comes of one of our proofs: For every sufficiently large n there is a prime $\text{p < n}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ with [$\text{n}\text{p}$] composite.     

On groups with relatively small normalizers of nonabelian subgroups

We investigate the structure of a finite nonsolvable group G in which the index |N _G (A): AC _G (A)| is either one or a prime for any nonabelian subgroup A.     

Artinian rings with supersolvable adjoint group

The set of all elements of an associative ring R, not necessarily with a unit element, forms a monoid under the circle operation a ° b = a + b + ab. The group of all invertible elements of this monoid is called the adjoint group of R and is denoted by R ^°. It is proved that an artinian ring R with supersolvable adjoint group R ^° must be Lie supersolvable. An example of a Lie supersolvable ring with non-supersolvable adjoint group is also constructed. Received: 7 December 2007     

On finite groups with relatively large centralizers of invariant subgroups

In the paper, the finite groups G are studied for which every invariant subgroup A has the property that |G: AC _G (A)| divides a fixed prime p.     

On the solvability of a group with permutable subgroups

The solvability of a finite group G = AB is established under the assumption that the subgroups A and B are solvable and the Carter subgroups of A commute with the Carter subgroups of B.     

On Hall subgroups of a finite group

New criteria of existence and conjugacy of Hall subgroups of finite groups are given.     

On generalized m-S-permutable subgroups of a finite group

In this paper, we give some new conditions under which a normal subgroup E of a finite group G is hypercyclically embedded in G, that is, every chief factor of G below E is cyclic.     

On sums of three integers with a fixed number of prime factors

Let N be sufficiently large odd integer. It is proved that the equation N=n₁+n₂+n₃ has solutions, where n_i has a fixed number of prime factors, and an asymptotic formula holds for the number of representations.     

On the intersection of subgroups of a free group

Summary The Hanna Neumann Conjecture says that the intersection of subgroups of rankn+1 andm+1 of a free group has rank at mostnm+1. This paper proves the conjecture for the casem=1. (See Theorem 1.) Our methods imply that the strengthened Hanna Neumann Conjecture is also true in this case (Theorem 2).Oblatum 31-V-1991 & 8-X-1991     

On the number of cyclic subgroups of a group

Abstract

There has been some interest in understanding the relationship between the number of cyclic subgroups of a group and its order. This relationship is controlled in many cases by the size of the set of non-squares of the group. We improve upon previously established bounds and classify groups that obtain our new bound.     

On s-quasinormal and c-normal subgroups of a finite group

Let F be a saturated formation containing the class of supersolvable groups and let G be a finite group. The following theorems are shown： （1） G ∈ F if and only if there is a normal subgroup H such that G/H ∈ F and every maximal subgroup of all Sylow subgroups of H is either c-normal or s-quasinormally embedded in G; （2） G ∈F if and only if there is a soluble normal subgroup H such that G/H∈F and every maximal subgroup of all Sylow subgroups of F（H）, the Fitting subgroup of H, is either e-normally or s-quasinormally embedded in G.