Number

A number is a mathematical object used to count, measure and label. The most basic examples are the natural numbers, 1, 2, 3 and so on, which can be represented in spoken or written language with number words or with symbols called numerals; a numeral system such as the Hindu-Arabic decimal system lets any non-negative integer be written with a fixed set of ten digit symbols. Over the centuries mathematicians extended the concept of number to include zero, negative numbers, rational numbers such as one half, real numbers such as the square root of two and pi, and complex numbers, which add a square root of negative one to the real numbers. Calculations with numbers use arithmetical operations such as addition, subtraction, multiplication, division and exponentiation, and the study of the properties of numbers is called number theory. During the nineteenth century mathematicians began developing algebraic structures that share properties with numbers and can be seen as extending the concept further, though whether a given structure such as the p-adic numbers or the hypercomplex numbers is itself called a number is more a matter of convention than a strict mathematical distinction. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/