magic number

English Thesaurus

1. the atomic number of an extra stable strongly bound atomic nucleus: 2, 8, 20, 28, 50, 82 or 126 (noun.quantity)

hypernym	:	atomic number,
definition	:	the order of an element in Mendeleyev's table of the elements; equal to the number of protons in the nucleus or electrons in the neutral state of an atom of an element (noun.quantity)