  We prove that if $x$ is large enough, namely $x\ge x_0$, then there exists a
prime between $x(1- \Delta^{-1})$ and $x$, where $\Delta$ is an effective
constant computed in terms of $x_0$. This improves some previous results of
Ramar\'e and Saouter and is used to verify the Ternary Goldbach Conjecture for
the integers up to $7.86\cdot 10^{27}$.
