These numbers are one of the oldest, most universal concepts of mathematics. Number theory is the study of properties of the natural numbers. One of the central issues of number theory is that of factorization and in

particular prime numbers. A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. Thus, the prime numbers are

2, 3, 5, 7, 11, 13, 17, . . . .