https://katex.org/docs/supported.html
1.x_n $x_n$
2 . \sum $\sum$
\sum_{i=1}^n $\sum_{i=1}^n $
3.\binom{n}{k} $\binom{n}{k}$
4. \leq $\leq$
5.\geq $\geq$
6.\sqrt{x} $\sqrt{x}$
