A prime number is any positive integer greater than zero that has only two proper divisorsNumber that when divided into another number leaves no remainder. , 1 and the number itself. Thus the lowest prime number is 2, which is also the only even prime;[a]One is not a prime number because it has only one proper divisor, itself. numbers greater than 1 that are not prime are known as composite numbers, because they can be expressed as the product of two other numbers smaller than themselves;[1] for instance, 8 can be expressed as 2 × 4.
Prime numbers are fundamental to mathematics, as all whole numbers can be constructed from them; anything that can be shown to be true about prime numbers is therefore true for all numbers.[2]
Two numbers are considered to be relatively prime, or coprime, if their greatest common divisor is 1. For example, 9 and 28 are coprime, despite neither being a prime number.[3]
Notes
| a | One is not a prime number because it has only one proper divisor, itself. |
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