What numbers have at least 6 factors?

Answer 1

That's an infinite list. Here are several: 45, 63, 75, 99

Answer 2

The products of a square of a prime and a prime.

That is, if a and b are primes, all numbers of the form a2b will have 6 factors.

The 6 factors will be : 1, a, a2, b, ab, a2b

Answer 3

That's an infinite list; much too long to print here.

Answer 4

That's an infinite list. It includes every Prime number to the 5th power, like 32 and 243.