Before revision: This article could never hope to be comprehensive, but there are some generalisations possible.
After revision: The number of series and parallel combinations that can be formed grows exponentially with the number of resistors, n. For large n the size of the set has been found by numerical techniques to be approximately 2.53n and analytically strict bounds are given by a Farey sequence of Fibonacci numbers.Khan, p.154This article could never hope to be comprehensive, but there are some generalisations possible.