1. Introduction. The aim of this paper is to supply a still better result for the problem considered in [2]. Let A(x) denote the number of distinct abelian groups (up to isomorphism) of orders not exceeding x. We shall prove Theorem 1. For any ε > 0, $A\left(x\right)=C₁x+C₂x^{1/2}+C₃x^{1/3}+O\left(x^{50/199+\epsilon }\right)$, where C₁, C₂ and C₃ are constants given on page 261 of [2]. Note that 50/199=0.25125..., thus improving our previous exponent 40/159=0.25157... obtained in [2]. To prove Theorem 1, we shall proceed along the line of approach presented in [2]....

Let$$T\left(x\right)=K_{1}x{log}^{2}x+K_{2}xlogx+K_{3}x+\Delta \left(x\right),$$where $T\left(x\right)$ denotes the number of subgroups of all abelian groups whose order does not exceed $x$ and whose rank does not exceed $2$, and $\Delta \left(x\right)$ is the error term. It is proved that$${\int }_1^X{\Delta }^2\left(x\right)dx\ll X^2{log}^{31/3}X,{\int }_1^X{\Delta }^2\left(x\right)dx=\Omega \left(X^2{log}^{4}X\right).$$

A subset $S$ of a finite abelian group, written additively, is called zero-sumfree if the sum of the elements of each non-empty subset of $S$ is non-zero. We investigate the maximal cardinality of zero-sumfree sets, i.e., the (small) Olson constant. We determine the maximal cardinality of such sets for several new types of groups; in particular, $p$-groups with large rank relative to the exponent, including all groups with exponent at most five. These results are derived as consequences of more general...

We study the structure of longest sequences in $\mathbb{Z}{ₙ}^d$ which have no zero-sum subsequence of length n (or less). We prove, among other results, that for $n=2^a$ and d arbitrary, or $n=3^a$ and d = 3, every sequence of c(n,d)(n-1) elements in $\mathbb{Z}{ₙ}^d$ which has no zero-sum subsequence of length n consists of c(n,d) distinct elements each appearing n-1 times, where $c(2^a,d)=2^d$ and $c(3^a,3)=9$.

From a paper by A. Angelakis and P. Stevenhagen on the determination of a family of imaginary quadratic fields $K$ having isomorphic absolute Abelian Galois groups $A_K$, we study any such issue for arbitrary number fields $K$. We show that this kind of property is probably not easily generalizable, apart from imaginary quadratic fields, because of some $p$-adic obstructions coming from the global units of $K$. By restriction to the $p$-Sylow subgroups of $A_K$ and assuming the Leopoldt conjecture we show that the...

In this paper we consider completely decomposable torsion-free groups and we determine the subgroups which are ideals in every ring over such groups.