A **number** is a mathematical object used to count, label, and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers.

Mathematical operations are certain procedures that take one or more numbers as input and produce a number as output. Unary operations take a single input number and produce a single output number. For example, the successor operation adds one to an integer, thus the successor of 4 is 5. Binary operations take two input numbers and produce a single output number. Examples of binary operations include addition, subtraction, multiplication, division, and exponentiation. The study of numerical operations is called arithmetic.

A notational symbol that represents a number is called a numeral. In addition to their use in counting and measuring, numerals are often used for labels (telephone numbers), for ordering (serial numbers), and for codes (e.g., ISBNs).

In common use, the word *number* can mean the abstract object, the symbol, or the word for the number.

Read more about Number: Classification of Numbers, Numerals

### Famous quotes containing the word number:

“To make life more bearable and pleasant for everybody, choose the issues that are significant enough to fight over, and ignore or use distraction for those you can let slide that day. Picking your battles will eliminate a *number* of conflicts, and yet will still leave you feeling in control.”

—Lawrence Balter (20th century)

“God ... created a *number* of possibilities in case some of his prototypes failed—that is the meaning of evolution.”

—Graham Greene (1904–1991)

“[The] elderly and timid single gentleman in Paris ... never drove down the Champs Elysees without expecting an accident, and commonly witnessing one; or found himself in the neighborhood of an official without calculating the chances of a bomb. So long as the rates of progress held good, these bombs would double in force and *number* every ten years.”

—Henry Brooks Adams (1838–1918)