AZX notation describes any nucleus

Atomic Structure & Nuclear Stability — AQA A-Level Physics

A nucleus is written as ${}_{Z}^{A}X$ where $X$ is the chemical symbol.
The top number $A$ is the nucleon number (mass number) — total protons + neutrons.
The bottom number $Z$ is the proton number (atomic number) — total protons.
Number of neutrons $= A - Z$.

Examiner Tips and Tricks

In chemistry, nucleon number is called 'mass number' and proton number is called 'atomic number'.
Both are valid.
Just don't confuse them.