At the wikipedia page for the Möbius function http://en.wikipedia.org/wiki/M%C3%B6bius_function there is an expression for the ordinary generating function for the Möbius function.
Is it possible to calculate the radius of convergence for any of the terms in the expression?
For example what would the radius of convergence for the double sum be: $\sum_{a=2}^{\infty} \sum_{b=2}^{\infty} x^{a*b}$
Or the triple sum: $\sum_{a=2}^{\infty} \sum_{b=2}^{\infty} \sum_{c=2}^{\infty} x^{a*b*c}$