Zentralblatt MATH

Publications of (and about) Paul Erdös

Zbl.No:  699.10068
Autor:  Erdös, Paul; Sárközy, A.
Title:  On a conjecture of Roth and some related problems. II. (In English)
Source:  Number theory, Proc. 1st Conf. Can. Number Theory Assoc., Banff/Alberta (Can.) 1988, 125-138 (1990).
Review:  [For the entire collection see Zbl 689.00005.]
Let A1,...,Ak be a partition of the set of natural numbers into disjoint classes, and let B be the set of integers that have a representation in the form aa' where a,a' in Ai for some i. It is proved that for a fixed number M the minimal number of elements (over all partitions) of B up to M is between M(log M)-\alpha and M(log M)-\beta with some constants 0 < \beta < \alpha, but sumb in B1/b > (c/k) log M with an absolute constant c > 0. The second result implies that for a fixed partition the upper density of B is > c/k, and it is proved that it can be < c'/k with another constant c'. The lower density is also positive, but it is proved that already for k = 3 it cannot be estimated from below from a positive constant independent of the concrete partition; for k = 2 this problem remains undecided.
The corresponding additive problem was investigated by the authors and V. T. Sos in Part I of this paper [Irregularities of partitions, Pap. Meet., Fertod/Hung. 1986, Algorithms. Comb. 8, 47-59 (1989; Zbl 689.10061)].
Reviewer:  I.Z.Ruzsa
Classif.:  * 11B83 Special sequences of integers and polynomials
Keywords:  products of integers; multiplicative representation; upper density; lower density
Citations:  Zbl 689.00005; Zbl 689.10061

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