Natural Numbers - A natural number is every number that comes after one in the counting system. It is any number that is used for counting purposes. Numbers that begin with one and have no fractional components are known as natural numbers. It is usually denoted by the letter N.  Whole Numbers - The set of whole numbers is the union of all natural numbers, including zero. This is the system of natural numbers, which includes the number zero, also known as the entire number system. It is usually denoted by the letter W.