An investigation of the numbers of isotopes of some particular elements seems to lead to the assumption that there is a simple numerical relationship among the number of isotpopes, the atomic number, and the period. If the atomic number of an element is divisible by the square root of twice the actual number(1) of elements which are contained by the same period that includes the element under consideration, the quotient, a whole number, will be equal to the number of naturally occurring isotopes of the element.