I forgot most things about factorials but now I have to use them again to simplify expressions while doing convergence tests... What I know is: [tex] (n +1) ! = (n +1) n! [/tex] [tex] (2n +1)! = (2n +1) 2n! ? [/tex] but I don't know how to deal with these: [tex] (n -1) ! = ?[/tex] [tex] (2n-1) ! = ?[/tex] Thanks for any help.