What is a prime number? A number is greater than 1 is called a prime number, if it has only two factors, 1 and the number itself.

According to the defination of prime number, the prime numbers between and 1 to 100 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97. They are total 25.