On the Pythagoras numbers of real analytic curves

We show that the Pythagoras number of a real analytic curve is the supremum of the Pythagoras numbers of its singularities, or that supremum plus 1. This includes cases when the Pythagoras number is infinite.      

On the distribution of sociable numbers

For a positive integer n, define s(n) as the sum of the proper divisors of n. If s(n)>0, define s₂(n)=s(s(n)), and so on for higher iterates. Sociable numbers are those n with sk(n)=n for some k, the least such k being the order of n. Such numbers have been of interest since antiquity, when order-1 sociables (perfect numbers) and order-2 sociables (amicable numbers) were studied. In this paper we make progress towards the conjecture that the sociable numbers have asymptotic density 0. We show that the number of sociable numbers in [1,x], whose cycle contains at most k numbers greater than x, is o(x) for each fixed k. In particular, the number of sociable numbers whose cycle is contained entirely in [1,x] is o(x), as is the number of sociable numbers in [1,x] with order at most k. We also prove that but for a set of sociable numbers of asymptotic density 0, all sociable numbers are contained within the set of odd abundant numbers, which has asymptotic density about 1/500.     

On characterizations of the ordered field of real numbers

This self-contained note could find classroom use in an introductory course on analysis. It is proved that an ordered field F is complete (that is, order-isomorphic to the field of real numbers) if and only if each bounded monotonic sequence in F converges in F. Also established is the key tool that an ordered field is complete if and only if it is Archimedean and Cauchy-complete, along with a number of characterizations of Archimedean fields.     

On localization of the characteristic numbers of real matrices

In this paper we give domains for the distribution on the complex plane of the characteristic numbers of a set of real matrices, basing our work on results obtained by F. I. Karpelevich for matrices with nonnegative elements.Translated from Matematicheskie Zametki, Vol. 15, No. 5, pp. 765–768, May, 1974.In conclusion the author expresses his thanks to R. A. Poluéktov and G. S. Épel'man for useful discussions of his work.     

On approximation of real numbers by algebraic numbers of bounded degree

Dirichlet proved that for any real irrational number ξ there exist infinitely many rational numbers p/q such that |ξ−p/q|<q⁻². The correct generalization to the case of approximation by algebraic numbers of degree ?n, n>2, is still unknown. Here we prove a result which improves all previous estimates concerning this problem for n>2.     

On distribution of semiprime numbers

A semiprime is a natural number which is the product of two (possibly equal) prime numbers. Let y be a natural number and g(y) be the probability for a number y to be semiprime. In this paper we derive an asymptotic formula to count g(y) for large y and evaluate its correctness for different y. We also introduce strongly semiprimes, i.e., numbers each of which is a product of two primes of large dimension, and investigate distribution of strongly semiprimes.     

On the transcendence of real numbers with a regular expansion

We apply the Ferenczi-Mauduit combinatorial condition obtained via a reformulation of Ridout's theorem to prove that a real number whose b-ary expansion is the coding of an irrational rotation on the circle with respect to a partition in two intervals is transcendental. We also prove the transcendence of real numbers whose b-ary expansion arises from a non-periodic three-interval exchange transformation.     

On the simultaneous rational approximations to real and p-adic numbers

Lithuanian Mathematical Journal - We consider simultaneous rational approximations to real and p-adic numbers. We prove that for any irrational number α0 and p-adic number α, there are...     

On the distribution of square-full and cube-full numbers

There are many results on the distribution of square-full and cube-full numbers. In this article the distribution of these numbers are studied in more detail. Suchk-full numbers (k=2,3) are considered which are at the same time 1-free (1k+2). At first an asymptotic result is given for the numberN _k,1(x) ofk-full and 1-free numbers not exceedingx. Then the distribution of these numbers in short intervals is investigated. We obtain different estimations of the differenceN _k,1(x+h)–N_k,1(x) in the casesk=2, 1=4,5,6,7,18 andk=3, 1=5,6,7, 18.     

On the densities of rational multiples

For two subsets of natural numbers \( A,B \subset \mathbb{N} \), define the set of rational numbers \( \mathcal{M}\left( {A,B} \right) \) with the elements represented by m/n, where m and n are coprime, m is divisible by some a ∈ A, and n is divisible by some b ∈ B. Let I be some interval of positive real numbers and \( \mathcal{F}_x^I \) denote the set of rational numbers m/n ∈ I such that m and n are coprime and n ? x. The analogue to the Erdös–Davenport theorem about multiples is proved: under some constraints on I, the limits \( {{{\sum {\left\{ {\frac{1}{{mn}}:\frac{m}{n} \in \mathcal{F}_x^I \cap \mathcal{M}\left( {A,B} \right)} \right\}} }} \left/ {{\sum {\left\{ {\frac{1}{{mn}}:\frac{m}{n} \in \mathcal{F}_x^I} \right\}} }} \right.} \) exist for all subsets \( A,B \subset \mathbb{N} \) as x → ∞.     

On the distribution of numbers of a special form

Translated from Matematicheskie Zametki, Vol. 55, No. 2, pp. 157–161, February, 1994.     

On the distribution of square-full numbers in arithmetic progressions

A positive integer n is called a square-full number if p ² divides n whenever p is a prime divisor of n. In this paper we study the distribution of square-full numbers in arithmetic progressions by using the properties of Riemann zeta functions and Dirichlet L-functions.