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