MathDB
sequence expressed as sum of 2 sequences

Source: ItaMO 2004, p5

March 4, 2012
number theory proposednumber theory

Problem Statement

Decide if the following statement is true or false: For every sequence {xn}nN\{x_n\}_{n\in \mathbb{N}} of non-negative real numbers, there exist sequences {an}nN\{a_n\}_{n\in\mathbb{N}} and {bn}nN\{b_n\}_{n\in\mathbb{N}} of non-negative real numbers such that: (a) xn=an+bnx_n = a_n + b_n for all nn; (b) a1++anna_1 + \cdots + a_n \le n for infinitely many values of nn; (c) b1++bnnb_1 + \cdots + b_n \le n for infinitely many values of nn.