What number do you get when you multiply the distinct (different) prime factors of 28?

The list of all factors of 28 is :

{1, 2, 4, 7, 14, 28 }, 

We can get this list by listing all the numbers up to 28, and eliminate the nonfactors.
 

Of the factors in the above set, the primes are {2, 7}

So, the when we multiply the prime factors of 28 we get:

2*7=14

14