IMC 2015 · Problem 3

Day 122nd IMC · Blagoevgrad, Bulgaria

Statement

Let F(0)=0F(0) = 0, F(1)=32F(1) = \frac{3}{2}, and F(n)=52F(n1)F(n2)F(n) = \frac{5}{2}F(n-1) - F(n-2) for n2n \ge 2.

Determine whether or not n=01F(2n)\sum\limits_{n=0}^{\infty} \dfrac{1}{F(2^n)} is a rational number.

Official solution

Hidden so you can work on the problem first.

Proposed by Gerhard Woeginger, Eindhoven University of Technology.