  This paper focuses on the Starobinsky model of inflation. We derive solutions
for various cosmological observables, such as the scalar spectral index $n_s$,
the tensor-to-scalar ratio $r$ and their runnings, as well as the number of
$e$-folds of inflation, reheating, and radiation with minimal assumptions. We
establish an equation that connects inflation and reheating, which can be
solved for the spectral index $n_s$. Using consistency relations of the model,
we determine the other observables, the number of $e$-folds during inflation
$N_k$, and the number of $e$-folds during reheating $N_{re}$. The impact of
reheating on inflation is explored by constraining the equation of state
parameter $\omega_{re}$ at the end of reheating. We find remarkable agreement
between the Starobinsky model and current measurements of the power spectrum of
primordial curvature perturbations and the present bounds on the spectrum of
primordial gravitational waves.
