1. The problem statement, all variables and given/known data Determine the accumulation points of the following set: z(sub n)=i^n, (n=1,2,....); 2. Relevant equations 3. The attempt at a solution My book says z(sub n) does not have any accumulation points. When mapped onto a complex plane, z(sub n) forms a circle. For any set to contained each of its accumulation points, the set has to be closed. And the definition of a closed set is a set containing all of its boundary points. z(sub n) is a close set since the only points of z(sub n) are: i,-1,-i and 1. How can any of those four points not be accumulation points?