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} $\sqrt{x}$