28. Let $p_{1}, p_{2}, p_{3}, \ldots, p_{n}$ be distinct prime numbers. How many divisors does the number $q=p_{1} p_{2} p_{3} \ldots p_{n}$ have, including 1 and $q$?
28. The divisors of the number $q$ are, obviously, the numbers $p_{1}, p_{2}, p_{3}, \ldots, p_{n}$ and all possible products of them taken two at a time, three at a time, and so on. The number of such divisors is $C_{n}^{0}+C_{n}^{1}+C_{n}^{2}+\ldots+C_{n}^{n}=2^{n}$. (This is the sum of the binomial coefficients).