Quora: IMO 1988 Question 3

Problem A3

A function f is defined on the positive integers by:

for all positive integers n,

$latex f(1) = 1 $
$latex f(3) = 3$
$latex f(2n) = f(n)$
$latex f(4n + 1) = 2f(2n + 1) – f(n) $
$latex f(4n + 3) = 3f(2n + 1) – 2f(n) $

Determine the number of positive integers n less than or equal to 1988 for which f(n) = n.

What is the explanation of the solution of problem 3 from IMO 1988? by Alon Amit

https://www.quora.com/What-is-the-explanation-of-the-solution-of-problem-3-from-IMO-1988/answer/Alon-Amit?share=7719956f&srid=oZzP