A set of positive integers can also be represented by N+, where n is a set of natural numbers. In mathematics, the capital symbol z is used to represent the set of all integers, including positive integers, 0 and negative integers. All integers form an integer set, which is a number ring. In the integer system, zero and positive integers are collectively called natural numbers. Z mathematically represents a set of integers, and Z+ represents a set of positive integers. Like an integer, a positive integer is a countable infinite set. In number theory, positive integers are 1, 2,3, but in set theory and computer science, natural numbers usually refer to non-negative integers, that is, the set of positive integers and 0. It can also be said that all natural numbers other than 0 are positive integers.