if n and p are different positive prime numbers, which of the integers (power 4 of n), (power 3 of p) and np has/have exactly 4 positive divisors?
a. (power 4 of n)
b. (power 3 of p)
c. np
d. np & (power 4 of n)
e. (power 3 of p) and np
which one, why? thanks!
My try
n^4 have 1, n, n^2, n^3, n^4 (Total 5)
p^3 have 1, p, p^2, p^3 (Total 4)
np have 1, n, p, np (Total 4)
Hence only 2 (p^3 and np) of them have 4 positive divisors. Therefore E is the right answer.
