A composite number, also called a composite number, is a positive integer that satisfies one of the following (equivalent) conditions:
1. is the product of two integers greater than 1;
2. There is a factor)； greater than 1 and less than itself;
3. There are at least three factors (factors);
4. It is neither 1 nor a prime number (prime number);
5. Non-prime numbers with at least one prime factor.
In an integer, the number divisible by 2 is even, and vice versa.
Irrational number is a number in real number that cannot be accurately expressed as the ratio of two integers, that is, infinite acyclic decimal. Such as the square root of pi 3.