Odd numbers are: 1, 3,5,7,9,1,13, 15, 17, 19.

Even numbers are: 2,4,6,8, 10, 12, 14, 16,18,20.

The prime numbers are: 2,3,5,7, 1 1, 13, 17, 19.

The composite numbers are: 6, 8, 9, 10, 12, 14, 15, 16, 18, 20.

Prime number:

Prime numbers are also called prime numbers. A natural number greater than 1 cannot be divisible by other natural numbers except 1 and itself, and is called a prime number; Otherwise it is called a composite number (it is stipulated that 1 is neither a prime number nor a composite number).

The number of prime numbers is infinite. There is a classic proof in Euclid's Elements of Geometry. It uses a common proof method: reduction to absurdity.

Complex attribute:

A natural number with only 1 and its own two factors is called a prime number. (For example, from 2÷ 1=2, 2÷2= 1, we can see that the factor of 2 is only 1 and itself 2, so 2 is a prime number.

On the contrary, it is a composite number: "Besides 1 and itself, there are other factors called composite numbers." For example, 4÷ 1=4, 4÷2=2, 4÷4= 1. Obviously, the factor of 4 is a composite number other than 1 and itself 4.

The prime numbers within 100 are 2,3,5,7, 1 1 3, 17,19,23,29,31.