natural number

Natural number can mean either a positive integer (, , , , ...) or a non-negative integer (, , , , , ...). Natural numbers have two main purposes: they can be used for counting ("there are 3 apples on the table"), or they can be used for ordering ("this is the 3rd largest city in the country"). Properties of the natural numbers related to divisibility, such as the distribution of prime numbers, are studied in number theory.