Possible Duplicate:
What would be the radius of convergence of $\sum\limits_{n=0}^{\infty} z^{3^n}$?
How would I find the radius of convergence for $\displaystyle\sum_{n=0}^\infty2^{-n}z^{n^2}$? Im not sure how to deal with the $z^{n^2}$ term.
I know the ratio test = $\displaystyle\limsup_{n\rightarrow \infty}|c_n|^\frac{1}{n}$ for $\displaystyle\sum_{n=0}^\infty c_n(z-z_0)^n$, but since I have the $z^{n^2}$ term, how would I deal with it? Is the ratio test I should use now be $\displaystyle\limsup_{n\rightarrow \infty}|c_{n^2}|^\frac{1}{n^2}$? If so, what exactly would $c_{n^2}$ be?