A number has only two divisors, 1 and itself. Such numbers are called prime numbers.

A number has other divisors besides 1 and itself. Such numbers are called composite numbers.

1 is neither prime nor composite.

Two numbers whose common divisor is only 1 are called prime numbers.

Every composite number can be written as the multiplication of several prime numbers, which are called prime factors of this composite number.

Multiplying several prime factors to represent a composite number is called prime factor decomposition. Prime factors are usually decomposed by short division.