Ramanujan's sum

English

Noun

1. Template:Lb A function, usually denoted c_q(n), of two positive integer variables q and n, defined by the formula $c_q(n)=\sum _{\genfrac{}{}{0ex}{}{1\le a\le q}{(a,q)=1}}{e}^{2\pi i\frac{a}{q}n},$, where (a, q) = 1 means that a only takes on values coprime to q. It is used in the proof of Vinogradov's theorem.