### Instruction: Give me a summary of how to determine if a number is prime or not.
### Input: A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order.
### Response: A prime number is a number greater than one that cannot be the product of two smaller numbers besides 1 and itself (e.g., the number 5 is prime because the only product of two smaller numbers is 5 and 1).