  The relation between the reheating temperature, the number of e-folds and the
spectral index is shown for the Starobinsky model and some of its descendants
through a very detailed calculation of these three quantities. The conclusion
is that for viable temperatures between $1$ MeV and $10^9$ GeV the
corresponding values of the spectral index enter perfectly in its $2sigma$
C.L., which shows the viability of this kind of models.
