A prime number must satisfy three conditions: it must be a natural number (so numbers like 1.2, -7, or √3 are out of the question); it must be greater than 1; it must not be the product of any two other numbers. So essentially, a prime number is any natural number starting from 2 that isn’t divisible with any numbers other than 1 or itself. For instance: 5 is a prime number, it can only be written as a product of 1 x 5; 6 is not a prime number, it can be written as 2×3. A number that is not prime is called primes or Understanding the basics of prime numbers