2. Complex number: an integer greater than 1. If there are other divisors besides 1 and itself, such numbers are called composite numbers.
3. Odd number: Odd number, also known as odd number, is an important number, that is, an integer that is not divisible by 2. Odd numbers are often expressed as 2n+ 1 or 2n- 1, where n is an integer.
4. Even number: Even number, also called even number, is an important number, that is, an integer divisible by 2. Even numbers are usually expressed as 2n, where n is an integer. The sum, difference and product of even numbers are even numbers.
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From the concepts of prime number and composite number, we can know that 1 is neither a prime number nor a composite number among non-zero natural numbers. Historically, 1 was included in the prime number, but later, for the sake of fundamental theorem of arithmetic, 1 was finally excluded from the prime number by mathematicians. In primary school, students learn prime numbers and composite numbers, laying the foundation for finding the greatest common factor, the least common multiple, divisor and total score in future study.
In number theory, prime numbers play an important role and have always attracted many mathematicians to explore. 2500 years ago, the ancient Greek mathematician Euclid proved that the number of prime numbers is infinite, and proposed that a few prime numbers can be written as "2 to the nth power minus1"-where n is also a prime number. Since then, many mathematicians have studied this kind of prime number. /kloc-Mei Sen, a French priest in the 0/7th century, was one of them. He made outstanding achievements, so later generations called this prime number Mason prime number in the form of "2 minus 1".