This means by DeMoivre's Theorem, the focus root is
But there must be exactly roots, all spaced evenly about a circle.
So that means any can be written as
, where is a positive integer no greater than .
But any integer multiple of gives the same result as .
So that means .
Now let's go back to the original problem...
We have .
This is a geometric series with and .
So the sum is
So that means the sum is