For any three numbers x,y,z from the list.
Take any two you get x + y +xy = (1+x)(1+y) - 1
Take (1+x)(1+y) - 1 with z and get (((1+x)(1+y) - 1) + 1)(1+z) - 1
So combining any three numbers will give formula (1+x)(1+y)(1+z) - 1
By induction can we prove for combining list of any n numbers in ANY order its (1+x1)(1+x2)(1+x3)……(1+xn) - 1?