Let d⩾4 and c∈(−d,d) be relatively prime integers. We show that for any sufficiently large integer n (in particular suffices for 4⩽d⩽36), the smallest prime 43aee4"> with p⩾(2dn−c)/(d−1) is the least positive integer m with 2r(d)k(dk−c) (k=1,…,n) pairwise distinct modulo m , where r(d) is the radical of d . We also conjecture that for any integer n>4 the least positive integer m such that is the least prime p⩾2n−1 with p+2 also prime.