A cubic Gauss sum is a character sum combining a multiplicative character of order 3 with a nontrivial additive character of a finite
field. For Eisenstein integers , with
, a primary prime
satisfies
. Let
be its cubic residue
character, extended by zero at zero, and let
and
. The normalized sum is
For nonzero residues, is the cube root of unity
congruent to
modulo
(Dunn and Radziwiłł 2024).