What is the least whole number that has exactly 9 factors, including 1 and itself?

If the whole number has exactly 9 (odd number) factors, it will have to be a perfect square.

All squares of primes have exactly three factors.

So start with perfect squares (skipping perfect squares of primes)

4^2=16 {1,2,4,8,16} 5 factors.

6^2=36 {1,2,3,4,6,9,12,18,36} 9 factors.

Answer: 36 is the least whole number that has exactly 9 factors.