"Magic numbers" are one of the more cutely named phenomenon in atomic physics. Certain numbers of nucleons are preferred over the others, causing isotopes with the correct numbers of neutrons and protons to possess added stability.
The known magic numbers are Z (atomic mass) or N (atomic number) = 2, 8, 28, 50, 82, and 126. The first several of these correspond to the elements Helium, Oxygen and Nickel, all of which are more common in the universe than immediately adjacent elements. Isotopes with magic atomic mass typically have increased stability.