MathDB
Easy number theory

Source: Dutch NMO 2000

October 22, 2005

Problem Statement

Let aa and bb be integers. Define aa to be a power of bb if there exists a positive integer nn such that a=bna = b^n. Define aa to be a multiple of bb if there exists an integer nn such that a=bna = bn. Let xx, yy and zz be positive integer such that zz is a power of both xx and yy. Decide for each of the following statements whether it is true or false. Prove your answers. (a) The number x+yx + y is even. (b) One of xx and yy is a multiple of the other one. (c) One of xx and yy is a power of the other one. (d) There exist an integer vv such that both xx and yy are powers of vv (e) For each power of xx and for each power of yy, an integer ww can be found such that ww is a power of each of these powers. (f) There exists a positive integer kk such that xk>yx^k > y.