en.wikipedia.org/wiki/Function_(mathematics)

In mathematics, a function is a relation between a set of inputs and a set of
permissible outputs with the property that each input is related to exactly one
output.

functions.wolfram.com/

The world's largest collection of formulas and graphics about more than 300000
mathematical functions for the mathematics and science communities.

www.mathsisfun.com/sets/function.html

But we are not going to look at specific functions ... ... instead we will look at the
general idea of a function. Names. First, it is useful to give a function a name.

www.khanacademy.org/math/algebra/algebra-functions

Functions are mathematical entities that assign unique outputs to given inputs.
Sounds simple? Think again! In this topic you will evaluate, graph, analyze, and ...

www.khanacademy.org/math/algebra/algebra-functions/evaluating-functions/v/what-is-a-function

Functions assign a single unique output for each of their inputs. In this video, we
see examples of various kinds of functions.

dlmf.nist.gov/

Result of a project to provide a modern revision of Abramowitz and Stegun's "
Handbook of Mathematical Functions". The site includes definitions, properties,
and ...

tutorial.math.lamar.edu/Classes/Alg/FunctionDefn.aspx

This seems like an odd definition but we'll need it for the definition of a function (
which is the main topic of this section). However, before we actually give the ...

www.thefreedictionary.com/mathematical function

Noun, 1. mathematical function - (mathematics) a mathematical relation such that
each element of a given set (the domain of the function) is associated with an ...

helpx.adobe.com/coldfusion/cfml-reference/coldfusion-functions/functions-by-category/mathematical-functions.html

Mathematical functions. Search. Search. Applies to: ColdFusion. Function,
Description ... Pi, Gets the mathematical constant pi, accurate to 15 digits.

msdn.microsoft.com/en-us/library/ms177516.aspx

Date and Time Data Types and Functions (Transact-SQL) ... All mathematical
functions, except for RAND, are deterministic functions. This means they return
the ...