Integers with exactly 4 odd factors and no even factors are perfect squares of prime numbers. To find these integers less than 100, we can list out the squares of prime numbers less than 10, as any prime greater than 10 squared would exceed 100.
The prime numbers less than 10 are: 2, 3, 5, 7.
The squares of these primes are: 4, 9, 25, 49.
So, the integers less than 100 with exactly 4 odd factors and no even factors are 4, 9, 25, and 49. There are four such integers.
