Adding Up Sequences of Towers

You are given an array A consisting of prime numbers greater than 4. Fun( Sequence S ) { if ( S has only 1 element ) return A[S[1]] X = S[2...last element] return power( A[S[1]] , Fun(X) ) } where power(A, B) returns AB, and A is 1-indexed. Fun(S) : Now you need to find the sum of the values returned by Fun(S) for every distinct sequence S. Each element of S is an integer from 1 to N. Thu