If in Rabin cryptosystem we have $n = p \cdot q$ where $p$ and $q$ is prime we have four solutions (roots) - exist four solution of $x^2 \equiv b \pmod{n}$.
However, when we have:
$n = p \cdot q \cdot r$
where $p$ and $q$ and $r$ is prime or:
$n = p \cdot q \cdot r \cdot z$
where $p$ and $q$ and $r$ and $z$ is prime
How much will we have solutions?
will they be $2^k$? where $k$ is the number of prime numbers?