Factorial in Wolfram Mathematica

Example for versions Wolfram Mathematica 8.0.4

This example uses recursive factorial definition. The first line defines Fact function. Note that the names of function arguments must have an underscore _ appended to them. 

Fact[n_] := If[n == 0, 1, Fact[n - 1]*n];
For[i = 0, i <= 16, i++, Print[i, "! = ", Fact[i]]];