To be precisely, let $f$ be a $C^\infty$ function defined on $(-\epsilon,\epsilon)$, where $\epsilon>0$.
Question: Can the power series $\sum_{n=0}^\infty\frac{f^{(n)}(0)}{n!}x^n$ have convergent radius $R=0$?
I think there might be some example satisfies $R=0$, but I cannot construct it, since it must be some non-elementary function and cannot be writen down in simple formula.
Any comments and ideas are welcome.