Greek symbols --Latex

$\propto$     \propto

$\infty$   \infty

$\ne$   \ne

$\approx$     \approx

$\sim$ :    \sim  --- same order of magnitude

$\bar{a}$   \bar{a}
https://en.wikipedia.org/wiki/List_of_mathematical_symbols

$\prod$, \prod   :: products of sequences, Capital Pi notation,