Several rules help predict nuclear stability. It turns out that certain numbers of protons or of neutrons are specially stable: 2, 8, 20, 28, 50, 82, and 126 are the magic numbers. Protons and neutrons are treated separately. The sum is not the important number. Even numbers are more stable than odd numbers. When those two rules don't predict, then nearness to the belt of stability predicts. For light (Z < 30) elements, the n/p ratio will be slightly above unity. Also used above, this Chart of Nuclides [local] chart gives an indication of a region of stability. (See dark squares within the predominantly red array of spots.)