Riho Terras (1939–2005) was an Estonian-American mathematician. He was born in

Tartu, Estonia Tartu is the second largest city in Estonia after the Northern European country's political and financial capital, Tallinn. Tartu has a population of 91,407 (as of 2021). It is southeast of Tallinn and 245 kilometres (152 miles) northeast o ...

and moved to

Ulm, Germany Ulm () is a city in the German state of Baden-Württemberg, situated on the river Danube on the border with Bavaria. The city, which has an estimated population of more than 126,000 (2018), forms an urban district of its own (german: link=no, ...

before starting school. In 1951 he migrated to

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

along with his mother. In 1965, he was given the Milton Abramowitz award for his studies at the

University of Maryland The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of M ...

. He finished his PhD in 1970 at the

University of Illinois Urbana-Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Univers ...

. He is known for the ''Terras theorem'' about the

Collatz conjecture The Collatz conjecture is one of the most famous unsolved problems in mathematics. The conjecture asks whether repeating two simple arithmetic operations will eventually transform every positive integer into 1. It concerns sequences of integ ...

, published in 1976, which proved that the conjecture holds for "almost all" numbers and established bounds for the conjecture. He married fellow mathematician

Audrey Terras Audrey Anne Terras (born September 10, 1942) is an American mathematician who works primarily in number theory. Her research has focused on quantum chaos and on various types of zeta functions. Early life and education Audrey Terras was born Sep ...

References

Estonian emigrants to the United States 1939 births 2005 deaths Estonian mathematicians 20th-century Estonian scientists 20th-century American mathematicians University of Maryland, College Park alumni University of Illinois Urbana-Champaign alumni {{Mathematician-stub