chip i think its because in terms of prime factorization a number that has exactly 16 factors has to look like one of the following:
16*1 = p^15
4*4 = p^3*q^3
2*2*2*2 = pqrs
4*2*2 = p^3*qr
8*2= p^7*q
looking at these i checked them out and using the smallest primes i figured the first and last ones to be way too big, but
2^3*3^3 = 216
2*3*5*7 = 210
2^3*3*5 = 120
so 120 must be the smallest whole number that has exactly 16 factors...right?