Dennis Arnold Hejhal (born December 10, 1948 in Chicago) is an American mathematician. In his mathematical research he frequently uses extensive computer calculation. In 1967, as a college freshman, Hejhal scored among the top 5 in the U.S. in the William Lowell Putnam Mathematical Competition.Hejhal graduated from the University of Chicago in 1970 with a bachelor's degree and from Stanford University in 1972 with a PhD in mathematics under the direction of Menahem Max Schiffer. He became an assistant professor at Harvard in 1972, then in 1974 an associate professor at Columbia University and starting in 1978 a professor at the University of Minnesota. Additionally, he was a professor at the University of Uppsala from 1994 to 2012 (where he has since been a professor emeritus) and a fellow