yes mass can be a number

Number of neutrons = Mass number - atomic number

The formula for mass number is number of neutrons = mass number - atomic number. Mass number can also be referred to as nucleon number.

Atomic mass is the number of protons in an atom

mass number is the number of protons plus neutrons in an atom

the number of neutrons would equal the mass number minus the atomic number.

The atomic weight of uranium is 238,02891(3) atomic mass units.

The mass number is the total number of nucleons (protons an neutrons) in the nucleus; the mass number is different for each isotope:

234U: mass number 234

235U: mass number 235

238U: mass number 238