Factorial

<%
    ' ASP Mathematics Library - Factorial
    '
    ' Copyright (c) 2008, reusablecode.blogspot.com; some rights reserved.
    '
    ' This work is licensed under the Creative Commons Attribution License. To view
    ' a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or
    ' send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California
    ' 94305, USA.
 
    ' Determine the factorial for a given number
    function factorial(x)
        dim result
 
        result = 1
 
        if x > 1 then
            for i = 2 to x
                result = result * i
            next
        end if
 
        factorial = result
    end function
 
    ' Returns the number of combinations, without regard to order, of y items that can be made from a pool of x items.
    ' Requires factorial()
    function combinatorial(x, y)
        if (x >= y) and (y > 0) then
            combinatorial = factorial(x) / factorial(y) / factorial(x - y)
        else
            combinatorial = 0
        end if
    end function
 
    ' Returns the number of permutations, with regard to order, of y items that can be made from a pool of x items.
    ' Requires factorial()
    function permutations(x, y)
        permutations = factorial(x) / factorial(x - y)
    end function
%>