Prove the existence of a constant $c$$>0$,such that for every prime number there are at most $cp^{2/3}$ positive integers $n$,for which $n!$$+1$ is divisible by $p$.
If, for every prime $p$, the set of integers with the property is {${a_1,...,a_k}$} we have that there are at most $s$ differences between $a_i$ and $a_j$ equal to $s$, but I can't continue.