Gauss sum
As is discussed in more detail below, the Gaussian periods are closely related to another class of sums of roots of unity, now generally called Gauss sums (sometimes Gaussian sums). The quantity "P" − "P"* presented above is a quadratic Gauss sum mod "p", the simplest non-trivial example of a Gauss sum. One observes that "P" − "P"* may also be written as