What is a complex number? What are the plural numbers?

Composite number refers to the number divisible by other numbers (except 0) except 1 and itself in natural numbers. In contrast, it is a prime number, and 1 is neither a prime number nor a composite number. The smallest composite number is 4. Among them, the perfect number and the number of blind dates are based on this.

1, all even numbers greater than 2 are composite numbers.

2. In all odd numbers greater than 5, all numbers with 5 are composite numbers.

3. Except 0, all natural numbers whose unit is 0 are composite numbers.

4. All natural numbers with units of 4, 6 and 8 are composite numbers.

5. The smallest (even) complex number is 4, and the smallest odd complex number is 9.

6. Every composite number can be written as the unique form of the product of prime numbers, that is, the factorization of prime factors. (fundamental theorem of arithmetic)

7. For any composite number greater than 5. (Wilson theorem)

Extended data:

One method of composite number is to calculate the number of prime factors. The sum of two prime factors is called semi-prime, and the sum of three prime factors is called wedge number. In some applications, composite numbers can also be divided into composite numbers of odd prime factors and composite numbers of even prime factors. For the latter, (where μ is Mobius function and'' x'' is half the number of prime factors), while the former is?

Note that for prime numbers, this function returns-1, while? . For the number "n" with one or more repeated prime factors,? .

Another way to classify composite numbers is to calculate the number of their factors. All composite numbers have at least three factors. What are the factors of prime square? . If a number has more factors than its small integer, it is called a high composite number. In addition, the number of factors of a complete square number is odd, and other composite numbers are even.

Composite numbers can be divided into odd and even numbers, basic composite numbers (divisible by 2 or 3), negative composite numbers (6N- 1) and positive composite numbers (6N+ 1), two-factor composite numbers and multi-factor composite numbers.

References:

Baidu encyclopedia-composite number