I'm wondering why the function $$ \frac{z(z^2-\pi^2)}{\sin(z)} $$ has a nonisolated singularity at infinity? I can identify the singularities which are removable or simple poles here, but sometimes I'm confused with how to discuss the case at infinity.
Thanks for the help!
No, $\infty$ is not an isolated singularity, since every natural number greater than $1$ is a singularity too.