Here are two examples of geometric series' with R=-1 and the number
of terms N is odd:
2,-2,2,-2,2,-2,2
The nth or 7th term, 2, is the same as the first term, 2.
Another example
-8,8,-8,8,-8
The nth or 5th term, -8, is the same as the first term, -8.
That'll always be the case.
Edwin