Hans Riesel

Hans Ivar Riesel, who lived from 28 May 1929 to 21 December 2014, was a Swedish mathematician born in Stockholm. In 1957 he used the computer BESK to discover the 18th Mersenne prime, a number of 969 digits with exponent 3217, and his prime held the record as the largest known prime from 1957 to 1961, until Alexander Hurwitz found a larger one. He also discovered the Riesel numbers and developed the Lucas-Lehmer-Riesel test, an extension of the Lucas-Lehmer primality test. After working at the Swedish Board for Computing Machinery he received his Ph.D. from Stockholm University in 1969 for a thesis titled Contributions to numerical number theory, and in the same year joined the Royal Institute of Technology as a senior lecturer and associate professor.