Does anyone know of the best estimates for $n_i$ and $n_{i+1}-n_i$ where $n_i$ is the $i-$th $y-$smooth number?

The best I could find was Tijdemann's estimate for the gap in terms of $\frac{n_i}{(log(n_i))^c}$ where $c$ is a constant depending on y.

For $n_i$ itself one could "invert" $\Psi(n_i,y)$ the estimate for number of smooth numbers, and get an estimate in terms if $i,$ but I wonder if it is worked out or if there is a better way.