Gauss sum of a Dirichlet character (source code)

= Gauss sum of a Dirichlet character
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{title2=$g(\chi)=\sum_{a\bmod N}\chi(a)e^{2\pi ia/N}$}

= Gauss sums of Dirichlet characters
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{synonym}

Extend a <Dirichlet character> by zero on nonunits. Its Gauss sum is $g(\chi)=\sum_{a\bmod N}\chi(a)e^{2\pi ia/N}$, and its finite Fourier transform at $r$ is $S_\chi(r)=\sum_{a\bmod N}\chi(a)e^{2\pi ira/N}$.