Vertex connectivity of the power graph of a finite cyclic group

Let $n=p_1^{n_1}{p}_2^{n_2}\dots p_r^{n_r}$, where $r,n_1,\dots ,n_r$ are positive integers and $p_1,p_2,\dots ,p_r$ are distinct prime numbers with $p_1<p_2<\cdots <p_r$. For the cyclic group $C_n$ of order $n$, let $\mathcal{P}(C_n)$ be the power graph of $C_n$ and $\kappa (\mathcal{P}(C_n))$ be the vertex connectivity of $\mathcal{P}(C_n)$. It is known that $\kappa (\mathcal{P}(C_n))=p_1^{n_1}-1$ if $r=1$. For $r\ge 2$, we determine the exact value of $\kappa (\mathcal{P}(C_n))$ when $2\phi(p_1\ldots p_{r-1})\geq p_1\ldots p_{r-1}$,andgiveanupperboundfor$\kappa($\mathcal{P}$(C_n))$when$2\phi(p_1\ldots p_{r-1}) < p_1\ldots p_{r-1}$, which is sharp for many values of $n$ but equality need not hold always.