The only numbers that have two divisors, themselves and one, are prime numbers. Prime numbers are always greater than one and are positive numbers.
Prime numbers are also called prime integers. Euclid showed around 300 B.C. that there are infinitely many prime numbers. Being a prime is referred to as a property and is called primality. There have been many algorithms built to try to predict and factor prime numbers and are normally referred to as prime factorization. These algorithms can vary in complexity, but there has yet to be one made that can be used for general purpose use. The opposite of a prime number is called a composite. All even numbers above the number two are considered composite because they have multiple positive integer divisors.