The concept of GRE mathematical integer 1. Natural number: a positive integer greater than zero. For example, 1, 2, 3,? Where 1 is a small natural number. 2. Odd number: an integer that is not divisible by 2. Such as: 1, 1, 3, -3...3. Even number: an integer divisible by 2. Such as: 0,2,12,4, -4. 4. Prime number: a natural number that is not divisible by other positive integers except I and itself, such as: 2, 3, 5, 7, 1 1 ... where 2 is a small prime number. 5. Complex number: Besides 1 and itself, there are natural numbers of other factors, such as 4, 6, 8, 9, 10 ""? Where 4 is a small composite number. (Eto International Education Tips: Prime numbers and composite numbers cannot be negative numbers, and 0 and 1 are neither prime numbers nor composite numbers. 6. Mutual prime numbers: If the greatest common divisor of two numbers is 1, then these two numbers are called prime numbers. For example: 13 and 15, 19 and 23, etc. 7. Multiplicity and divisibility: When an integer A can be divisible by another integer B, A is called a multiple of B, and B is called a divisor or divisor of A. For example, 10 is a multiple of 5, and 5 is a divisor of 10. 8. Common multiple: If a number is a multiple of several numbers at the same time, it is called their common multiple. The least common multiple is called the least common multiple. For example, 12, 24 and 36 are all common multiples of 2, 4, 6 and 12, where 12 is their small common multiple. 9. Common factor or divisor: If a number is a divisor of several numbers at the same time, it is called their common factor or common factor; The common divisor is called the greatest common factor or divisor. For example, 2,7, 14 are common divisors of 28,42,70, and 14 is their greatest common divisor. 10. Complete square: If an integer is still an integer after being squared, it is called complete square. Such as 4, 9, etc. Complete squares are natural numbers. Label: the concept of GRE mathematical integer