Class number related Peter Gustav Lejeune Dirichlet discovered formulas that relate the class number h of quadratic number fields to the Jacobi symbol. Source: Internet
Fourier did not, however, settle the question of convergence of his series, a matter left for Cauchy (1826) to attempt and for Dirichlet (1829) to handle in a thoroughly scientific manner (see convergence of Fourier series ). Source: Internet
Dirichlet has shown this for continuous, piecewise-differentiable functions (thus with countably many non-differentiable points). Source: Internet
Generalizations of the symbol include the Jacobi symbol and Dirichlet characters of higher order. Source: Internet
Another "Poisson's integral" is the solution for the Green function for Laplace's equation with Dirichlet condition over a circular disk: : where : : :φ is a boundary condition holding on the disk's boundary. Source: Internet
He had visited Dirichlet in 1852. Source: Internet