The Dirichlet kernel is obtained by integrating the number theoretic character over the ball ,
Dirichlet Kernel
See also
Delta Sequence, Dirichlet Integrals, Dirichlet's LemmaExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Dirichlet Kernel." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DirichletKernel.html