It is hard to learn how to learn mathematics.

$$\color{red}{``\text{All you need is that your brain is open"}}_{\text{Paul Erdos}}$$

Some of my favourite answers

(1) Polynomial outputs containing a particular Integer sequence

(2) Does $\Phi_n(\alpha)=0$ in $\Bbb{F}_p$ for some $\alpha\in\mathbb{F}_p$ imply that $\mathrm{ord}(\alpha) = n$?

(3) USA TST 2018/P1: Prove that the $n^{\text{th}}$ smallest positive integer relatively prime to $n$ is at least $\sigma(n)$