I'm a little bit confused that the number of irreducible polynomials of degree $n$ over $\mathbb{F}_{p}$.
In Dummit & Foote's textbook(Abstract algebra, 3rd), the number of $\textbf{irreducible}$ polynomials of degree $n$ over $\mathbb{F}_{p}$ is given by the following equation:$$\frac{1}{n}\cdot\sum_{d\mid n}\mu(d)\cdot p^{\tfrac{n}{d}}.$$
Is this only counting the number of $\textbf{monic irreducible}$ polynomials of degree $n$ over $\mathbb{F}_{p}$?
There is no constraint about $\textbf{monic}$ in the textbook. Can anyone help me? Thank you.