20th-century German mathematicians

Oskar Perron (7 May 1880 – 22 February 1975) was a German mathematician.
He was a professor at the University of Heidelberg from 1914 to 1922 and at the University of Munich from 1922 to 1951. He made numerous contributions to differential equations and partial differential equations, including the Perron method to solve the Dirichlet problem for elliptic partial differential equations. He wrote an encyclopedic book on continued fractions Die Lehre von den Kettenbrüchen. He introduced Perron's paradox to illustrate the danger of assuming that the solution of an optimization problem exists:

Let N be the largest positive integer. If N > 1, then N2 > N, contradicting the definition of N. Hence N = 1.

Gustav Doetsch (29 November 1892 – 9 June 1977) was a German mathematician, aviation researcher, decorated war veteran, and Nazi supporter.

Ludwig Georg Elias Moses Bieberbach (German: [ˈbiːbɐˌbaχ]; 4 December 1886 – 1 September 1982) was a German mathematician and Nazi.

Friedrich Wilhelm Daniel Levi (February 6, 1888 – January 1, 1966) was a German mathematician known for his work in abstract algebra, especially torsion-free abelian groups. He also worked in geometry, topology, set theory, and analysis.

Ernst Philipp Barthel (17 October 1890 in Schiltigheim - 16 February 1953 in Oberkirch (Baden)) was an Alsace philosopher, mathematician, and inventor.In the 1920s and 1930s he taught as a Privatdozent of philosophy at the University of Cologne. From 1924 on Barthel edited the magazine Antäus. Blätter für neues Wirklichkeitsdenken (Journal for new Reality Thinking), which served as the organ of the Gesellschaft für Lebensphilosophie (Society for Life Philosophy) founded by him in Cologne.
Barthel maintained philosophical friendships with his compatriots Albert Schweitzer and Friedrich Lienhard.

Heinrich Carl Franz Emil Timerding (23 January 1873 in Strasbourg – 30 April 1945 in Braunschweig) was a German mathematician, professor at the Braunschweig University of Technology, mainly known for his contributions to probability theory.
He was awarded the Brunswick and the Prussian War Merit Cross, the Ritterkreuz (Knight's Cross) of the Order of Henry the Lion, and in 1938 the Nazi Civil Service Faithful Service Medal.In 1900 he attended Columbia University in New York City the American Mathematical Society's summer meeting, where he read a paper.