maybe that´s a stupid question, however I could not find all the eingenvalues and eingenfunctions of the operator $D$, such that $D u= u_{rr} - \frac{n-1}{r}u_r $ for $u: \mathbb{R}^n \longrightarrow \mathbb{R}$. I don´t know exactly how to approach this problem even for $n= 3$.
Thanks in advance
