MathDB
n + f(f(n)) <= 2f(n) , strictly increasing

Source: 2013 Saudi Arabia IMO TST I p2

July 23, 2020
Increasingfunctioninequalitiesalgebra

Problem Statement

Let S=f{0.1.2.3,...}S = f\{0.1. 2.3,...\} be the set of the non-negative integers. Find all strictly increasing functions f:S→Sf : S \to S such that n+f(f(n))≤2f(n)n + f(f(n)) \le 2f(n) for every nn in SS
Back to ProblemsView on AoPS