There isn't a "formula" for atomic number. It's a fundamental property of an element, not calculated.

Here's what you need to know:

* Atomic number = Number of protons in an atom's nucleus.

* This number is unique to each element and defines its identity.

* It's represented by the symbol Z.

For example:

* Hydrogen (H) has an atomic number of 1 because it has 1 proton.

* Carbon (C) has an atomic number of 6 because it has 6 protons.

You can find the atomic number of any element on the periodic table. It's usually listed above the element's symbol.