What does the notation $11|a^2$ mean as used in this answer: https://math.stackexchange.com/a/948251/13230
I am trying to understand the proof that $\sqrt{11}$ is an irrational number, but am stuck when the following is stated:
This means that $11|a^2$ and so $11| a$ as $11$ is prime.
The notation means that "$11$ divides $a^2$." In other words it means there exists an integer $n$ such that $11n=a^2$.