sum of exponents: Omega

The number of prime factors of a given number, counting their multiplicity, is given by the upper case prime omega function, i.e., Ω. For example, Ω(12) = 3. Note that Ω(n) is synonymous with the sum of the exponents in the canonical prime factorization of n.
(The lower-case omega function gives the number of prime factors, IGNORING multiplicity.)
Here is the link to the Wikipedia article on this.
[Number Theory]
[counting functions]