Riho Terras (June 13, 1939 – November 28, 2005) was an Estonian-American mathematician. He was born in

Tartu, Estonia Tartu is the second largest city in Estonia after Tallinn. Tartu has a population of 97,759 (as of 2024). It is southeast of Tallinn and 245 kilometres (152 miles) northeast of Riga, Latvia. Tartu lies on the Emajõgi river, which connects the ...

, and moved to

Ulm, Germany Ulm () is the sixth-largest city of the southwestern German state of Baden-Württemberg, and with around 129,000 inhabitants, it is Germany's 60th-largest city. Ulm is located on the eastern edges of the Swabian Jura mountain range, on the up ...

, before starting school. In 1951, he emigrated to the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

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, United States. Founded in 1856, UMD is the flagship institution of the Univ ...

. He finished his PhD in 1970 at the

University of Illinois Urbana-Champaign The University of Illinois Urbana-Champaign (UIUC, U of I, Illinois, or University of Illinois) is a public university, public land-grant university, land-grant research university in the Champaign–Urbana metropolitan area, Illinois, United ...

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

Collatz conjecture The Collatz conjecture is one of the most famous List of unsolved problems in mathematics, unsolved problems in mathematics. The conjecture asks whether repeating two simple arithmetic operations will eventually transform every positive integer ...

, 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 S ...

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 {{Estonia-academic-bio-stub