Notation for every odd integer number I have this equation:

$$f(x)=\tan(x)$$

I found  the vertical asymptotes to be:

$$x=\frac{\pi}{2}k$$

What is the proper notation for that k is equal to every odd number integer(negative,positive, and zero)?
$$k\in\mathbb{Z}$$ is for every integer, but is there such a symbol for every odd number integer? 
Natural numbers are positive, and sometimes zero counting numbers, my question is about integers not natural numbers.

Usually people write:
$$\frac{\pi}{2}(2k+1), k \in \mathbb{Z}$$
Sometimes people would use  $\mathbb{O}$ for the set of all odd integers, but because it is not so standard they will tell you ahead of time:
$$\mathbb{O}=\{ 2n+1 : n \in \mathbb{Z}\}$$
So then, after defining $\mathbb{O}$, you would say:
$$\frac{\pi}{2}k, k \in \mathbb{O}$$
Get used the $\in$, it simply means  "is a member of" some set.
