What is the mathematical symbol for range?

You are looking for either:

1. A closed interval: $[a,b]$ represents the set of all real numbers greater or equal to $a$ and less or equal to $b$.

2. A integer interval: $[a\ldotp\ldotp b]$ represents all integers in between $a$ and $b$. ($[1\ldotp\ldotp 5] = \{1,2,3,4,5\}$)

This is a useful wikipedia reference.

It is important to make the distinction between whether or not a particular endpoint is included. Use ( or ) to exclude and [ or ] to include.

For instance

$$(a,b) \;\;\Rightarrow \;\; \{x\in\Bbb R:a<x<b\}$$ $$[a,b] \;\;\Rightarrow \;\;\{x\in\Bbb R:a\le x\le b\}$$ $$\{a..b\} \;\;\Rightarrow \;\;\{x\in\Bbb Z:a\le x\le b\}$$