A prime number is a natural number greater than 1, and it cannot be divisible by other natural numbers except 1 and itself. In other words, a number with no other factors except 1 is itself a prime number.

2 is the smallest prime number and the only number that is both even and prime. That is to say, all prime numbers are odd except 2, and there are 25 prime numbers less than 100: 2, 3, 5, 7, 1 1,13,65438.