  We compute the Morse index $\textsf{m}(u_{p})$ of any radial solution $u_{p}$
of the semilinear problem: \begin{equation} \label{problemaAbstract}\tag{P}
\left\{ \begin{array}{lr} -\Delta u=|x|^{\alpha}|u|^{p-1}u & \mbox{in } B\\ u=0
& \mbox{ on }\partial B \end{array} \right. \end{equation} where $B$ is the
unit ball of $\mathbb R^{2}$ centered at the origin, $\alpha\geq 0$ is fixed
and $p>1$ is sufficiently large. In the case $\alpha=0$, i.e. for the
\emph{Lane-Emden problem}, this leads to the following Morse index formula
\[\textsf{m}(u_{p}) = 4m^{2}-m-2, \] for $p$ large enough, where $m$ is the
number of nodal domains of $u$.
