Question 18
Let $a$ and $b$ be rational numbers such that $a+b = a^2 + b^2$. Suppose that the common value $s = a+b = a^2 + b^2$ is not an integer, and write it as an irreducible fraction: $s = \frac{m}{n}$. Let $p$ be the least prime divisor of $n$. Find the minimum value of $p$.