1. The problem statement, all variables and given/known data I have to find the general formula of the following series m=2, f(m)=1/45 m=3, f(m)=1/60 m=4, f(m)=2/175 m=5, f(m)=1/126 . . . 2. Relevant equations 3. The attempt at a solution I know that there exists some universal fitting models, such as, spline, RBFN and so on. However, the general formula should be monotonic with respect to m and simple in form. Hence, I can not appeal a universal fitting model.