Numerical Recipes in C is available free online. See Numerical Recipes Books On-Line
. It's a great resource. The site says:
Thanks to special permission from Cambridge University Press, we are able to bring you, free, the complete Numerical Recipes books in C, Fortran 77, and Fortran 90 On-Line, in Adobe Acrobat format. Due to copyright restrictions, Numerical Recipes in C++ is not available as part of this free resource.
The factorial representation is available at this PDF
(after a I chose LANL as the mirror site).