Problem

Source: I International Festival of Young Mathematicians Sozopol 2010, Theme for 10-12 grade

Tags: number theory



We will call the ordered pair $(a,b)$ “parallel”, where $a,b\in \mathbb{N}$, if $\sqrt{ab}\in \mathbb{N}$. Prove that the number of “parallel” pairs $(a,b)$, for which $1\leq a,b\leq 10^6$ is at least $3.10^6(ln\, 10-1)$.