Power series don't have to be centered at 0. They can be
centered at any point a, in which case the series will contain powers of (x−a) instead of x. If a power series centered at a has radius of convergence R, its interval of convergence will be from a−R to a+R.
Example: The power series ∞∑n=1(−1)n+1(x−1)nn
is centered at a=1. It has
a radius of convergence of 1, and an interval of convergence of (0,2]. (This series adds up to ln(x), by the way.)