A composite number is a positive integer greater than 1 that satisfies any of the following (equivalent) conditions:

1. It is the product of two integers greater than 1;

2. Have at least three positive factors;

3. A non-prime number with at least one prime factor.

4. The product of two or more prime numbers can form a composite number, and can only form a composite number. Conversely, a composite number can be decomposed into the product of a set of prime numbers, and can only be decomposed into the product of a set of prime numbers.

5. Any positive integer other than 1 that is not a prime number is a composite number.

, numbers that have other positive factors besides 1 and itself

Note: "0" and "1" are neither prime numbers nor composite numbers.

A natural number that has only two positive factors, 1 and itself, is called a prime number (or prime number). (For example, 2÷1=2, 2÷2=1, we know that the only factors of 2 are 1 and itself 2, so 2 is a prime number. The opposite of this is a composite number: "A number that has other factors besides 1 and itself is called a composite number." For example, 4÷1=4, 4÷2=2, 4÷4=1. Obviously, besides 1 and itself 4, 4 has another factor, 2, so 4 is a composite number.)

The prime numbers within 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, and 97. There are 25 prime numbers within 100.