Prime factors

Dear Mo2men,

My friend, good to hear from you! I hope you're well! I'm happy to respond.

First, let's look at the the prime factorizations, which I am sure you understand.
12 = 2*2*3
25 = 5*5
36 = 2*2*3*3
Here, 12 has 3 prime factors, 25 has 2 prime factors, and 36 has 4 prime factors. Sometimes, for clarity, this is called the "total number of prime factors." Of course, 36 needs a product of all four of those factors, both 2's and both 3's, to be 36.

We start talking about something very different when we discuss the "number of unique prime factors" or the "number of distinct prime factors" (the GMAT could use either terminology). Here, we want to know how many different prime factors divide into the number.
12 has two distinct prime factors: 2 and 3
25 has just one distinct prime factor: 5
36 has two distinct prime factors: 2 and 3
In fact, we could look at all the products of powers of 2 and powers of 3 (e.g. 72, 96, 144, 288, 324, 1296) also have just two distinct prime factors.

Does this make sense?
Mike