# Died: Prof. Dr. Hans-Egon Richert

On the 25th of November 1993, Professor Dr. Hans-Egon Richert died in Blaustein near Ulm, Germany, after a long and severe illness. Richert held a chair of Mathematics at the University of Ulm from 1972 until his retirement as an emeritus professor in 1991.

Richert was born 1924 in Hamburg and was raised there. He had to complete high school at a private institution after being expelled from the public school in the period of the Third Reich for "anglophile leanings".

In 1946, at last back in Hamburg after the war and military service, he could begin his studies of mathematics. He obtained his diploma after eight terms and his PhD only one year later. When his mentor, Professor Max Deuring, accepted a position in Göttingen, the young Richert joined him as an assistant and obtained the venia legendi there in 1954. Soon after he was put in charge of one of the best mathematical libraries in Germany.

After holding a temporary chair in Göttingen he was offered a newly created chair at the University of Marburg. In that time of vigorous development of the entire university system, Richert contributed in an essential way to shaping the Marburg Mathematical Institute, and, of course, he devoted his special love and attention to the library. From 1969 on, emotion held sway over reason in daily academic life in German universities, and especially so in Marburg. He was therefore pleased to accept in 1972 a chair at the young University of Ulm. His professorship here was the second one in the Mathematics Department, after that of Alexander Peyerimhoff. There was again much need for development.

Science had priority for Richert, teaching as well as research. Those who knew him from committee meetings recall that Richert spoke only when it was really necessary. He used to cut short a tedious discussion with a few well chosen and constructive - but never offensive - words. He also participated in reasonable administrative activities: in 1974/75 he served his university as Prorektor, then as a member of the unbeloved room allocation board, which in effect had to allocate shortages, and he acted for almost twenty years as chairman of the examination committee, an office that he administered unbureaucratically and always in the interest of the students.

Richert's field of research was Analytic Number Theory. He made important contributions to additive prime number theory, Dirichlet series, Riesz summability, the multiplicative analog of the Erdös-Fuchs theorem, estimates of the number of non-isomorphic abelian groups and bounds for exponential sums for use, e. g. in estimating the error term of the prime number theorem. From about 1965 on he focussed his research increasingly on sieve methods. Among other things he put the proof of Chen's p+P_2 theorem into readable form. An intensive research collaboration developed between Richert and Heini Halberstam, motivated by their common interest in sieves, and lasted for the rest of his life. The monograph on Sieve Methods that they coauthored immediately became the indispensable basis for research of many number theorists. Also, Richert's name was long associated with the best estimate for the Dirichlet divisor problem.

For many years he was one of the chairmen of the Oberwolfach meetings on Analytic Number Theory. The very high esteem he enjoyed in the mathematical community is reflected by the many invitations he received from mathematical institutions abroad, among others the University of Illinois at Urbana and the Tata Institute in Bombay.

His life was not confined to mathematics: Richert was also a stimulating conversational partner on many different subjects. He enjoyed exploring foreign countries and keeping records of his trips on film and tape, a pursuit that he followed with the same intensity as his science whenever time allowed.

In 1991 Professor Richert had to retire from his strenuous teaching duties. It is sad that he was not granted the long and fruitful period of retirement that he was looking forward to.

With the passing of Hans-Egon Richert we lose a treasured colleague and a researcher of international reputation.

Ulrike Vorhauer and Eduard Wirsing