How many three digit integers have 3 factors?

A three-digit integer has exactly three factors if it is the square of a Prime number. This is because the factors of ( p^2 ) (where ( p ) is a prime) are ( 1, p, ) and ( p^2 ). The three-digit squares of primes range from ( 11^2 = 121 ) to ( 31^2 = 961 ). The prime numbers in this range are 11, 13, 17, 19, 23, 29, and 31, totaling 7 three-digit integers that have exactly three factors.