These numbers are the atomic mass number, or nucleon number (top) and the electric charge (bottom), not the number of protons. Nuclear physicists use these particular numbers - rather than the number of a specific particle like protons - because in nuclear reactions, the atomic mass number and the electric charge are conserved, whereas particle counts are not. You can add up the values on top and on the bottom across a reaction and they should be the same on both sides, which provides a useful check for mistakes.
Fun fact: mass is not conserved during nuclear reactions, but the atomic mass number is not quite the mass, it's more like the mass rounded to the nearest integer number of atomic mass units. And the changes in mass during a nuclear reaction are small enough not to change the rounding. (Unless large quantities of antimatter are involved, but then you're way beyond the scope of nuclear physics.)