| Arnold Walfisz | |
| Birth Date: | 2 July 1892 |
| Birth Place: | Warsaw, Congress Poland, Russian Empire |
| Death Place: | Tbilisi, Georgian SSR, Soviet Union |
| Nationality: |  Poland |
| Fields: | Mathematics |
| Workplaces: | Tbilisi State University |
| Alma Mater: | University of Göttingen |
| Doctoral Advisor: | Edmund Landau |
| Known For: | Siegel–Walfisz theorem |
Arnold Walfisz (2 July 1892 – 29 May 1962) was a Jewish-Polish mathematician working in analytic number theory.
After the Abitur in Warsaw, Poland, Arnold Walfisz studied (1909−14 and 1918−21) in Germany at Munich, Berlin, Heidelberg and Göttingen. Edmund Landau was his doctoral-thesis supervisor at the University of Göttingen. Walfisz lived in Wiesbaden from 1922 through 1927, then he returned to Warsaw, worked at an insurance company and at the mathematical institute of the university (habilitation in 1930). In 1935, together with, he founded the mathematical journal Acta Arithmetica. In 1936, Walfisz became professor at the University of Tbilisi in Soviet Georgia. He wrote approximately 100 mathematical articles and three books.
By using a theorem by Carl Ludwig Siegel providing an upper bound for the real zeros (see Siegel zero) of Dirichlet L-functions formed with real non-principal characters, Walfisz obtained the Siegel–Walfisz theorem, from which the prime number theorem for arithmetic progressions can be deduced.
By using estimates on exponential sums due to I. M. Vinogradov and, Walfisz obtained the currently best O-estimates for the remainder terms of the summatory functions of both the sum-of-divisors function
\sigma
\phi