Hello. I've been trying to show that the function

$\displaystyle \displaystyle f(z)=\sum_{n=1}^\infty \frac{z^{n!}}{n}$

cannot be holomorphically extended outside the unit disk $\displaystyle D(0,1)$. I'd like to show that the function "blows up" at the boundary, but it isn't clear to me how to do that, except for simple points like $\displaystyle z=1, i,\ldots$

I'd appreciate any suggestions you may have.