The first 50 natural numbers are the integers between 1 and 50, including 1 and 50. The numbers that have an odd number of factors will be the perfect squares 1, 4, 9, 16, 25, 36, 49. The numbers that have exactly two factors will be the prime numbers (
all prime numbers have two factors, 1 and themself). The prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47...