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In 1859, German mathematician and number theorist Peter Gustav Lejeune Dirichlet passed away. Dirichlet made significant contributions to the field of mathematics, particularly in number theory and analysis. His work on Dirichlet's theorem on primes, Dirichlet characters, and the Dirichlet problem greatly influenced the development of these areas. He also introduced the concept of the Dirichlet function, which serves as an essential tool in mathematical analysis.