not a number

In a computer, not a number (usually abbreviated NaN) indicates that an arithmetical operation has resulted in a value that is not a number understood (or representable) by the computer. Division by zero is one frequent cause of a result being NaN. Asking for the square rootMathworldPlanetmath of a negative number is another operation that can result in NaN (unless the computer has been programmed to recognize imaginary numbersMathworldPlanetmath).

NaN is not a specific value that can be tested for with the usual comparison operators. The programmer is advised to test for NaN with a special function provided by the programming language (such as isNaN(x) in JavaScript.

Generally, computer algebra systems do not report NaN results even if they do display an error message for a given operation.


  • 1 David Flanagan, JavaScript the Definitive Guide: The Definitive Guide. New York: O‚ÄôReilly (2006): 24
Title not a number
Canonical name NotANumber
Date of creation 2013-03-22 18:14:09
Last modified on 2013-03-22 18:14:09
Owner PrimeFan (13766)
Last modified by PrimeFan (13766)
Numerical id 4
Author PrimeFan (13766)
Entry type Definition
Classification msc 68P01