Question 340307
If n and p are different positive prime numbers, which of the integers n^4, p^3 and np has (have) exactly 4 positive divisors?
<pre><b>
n<sup>4</sup> = nnnn has divisiors 1,n,nn,nnn,nnnn that's 5
p<sup>3</sup> = ppp has divisors 1,p,pp,ppp, that's 4
np has divisors 1,n,p,np, that's 4

So the answer is

(E) p<sup>3</sup> and np

Edwin