Abstract:
For the sum S of the Legendre symbols of a polynomial of odd degree n⩾3 modulo primes p⩾3, Weil's estimate |S|⩽(n−1)√p and Korobov's estimate
|S|⩽(n−1)√p−(n−3)(n−4)4forp⩾n2+92
are well known. In this paper, we prove a stronger estimate, namely,
|S|<(n−1)√p−(n−3)(n+1)4.