Set Builder Notation for Classifying Different Types of Sets Sets can be classified into several different types, each with unique properties and applications. The natural numbers, represented by the symbol N, consist of the counting numbers beginning with 1 and extending infinitely. These numbers can be expressed as {1, 2, 3, ...}, with the ellipsis signifying the infinite sequence of numbers that follows. The integers, represented by the symbol Z, encompass whole numbers, including negative nu