2014 USAJMO Problems/Problem 3
Let be the set of integers. Find all functions such that for all with .
Let's assume Substitute to get
This means that is a perfect square. However, this is impossible, as it is equivalent to Therefore, Now substitute to get Similarly, From these two equations, we can find either or Both of these are valid solutions on their own, so let's see if there are any solutions combining the two.
Let's say we can find and Then
If then which is only possible when This contradicts our assumption. Therefore, This forces due to the right side of the equation. Let's consider the possibility Substituting into the original equation yields which is impossible. So and there are no solutions "combining" and
Therefore our only solutions are and