What is a formula for the word mass number?

Question

i need a formula to describe mass number, or a sentence. a sentence would be great as well.

Answer 1

That is correct, here's why: Uranium 238

238 = # protons + # neutrons

92U - atomic # = # protons

The top number is the mass number which is the number of protons plus neutrons, which isn't always even.

Answer 2

Mass number is equal to the number of protons plus the number of neutrons in the nucleus.