Falling factorial

The falling factorial \((x)_n\) is defined as \(x \cdot (x - 1) \cdot (x - 2) \cdot \ldots \cdot (x - (n - 1))\).Falling Factorial from Wolfram MathWorld
==Examples==
\((x)_0\) = 1
\((x)_1\) = x 
\((x)_2\) = x(x-1) 
\((n)_n\)=n!
== Sources ==
== See also ==
Category:Functions
Category:Factorials