Universal way to convert from one base to another

Question

Is there a universal way to convert from one base to another? I know how to convert numbers with any base to decimal form. i.e., with $\sum_{i=0}^{n-1} r^{i}d_i$. However I don't know any universal way to convert from a number of any base to another number of any base. Does such a formula exist?

Answer 1

Formula you presented is universal for every base but the problem is that you must use sum function suitable for base you want to count.