Hans Ivar Riesel (born 1929 in Stockholm) is a Swedish mathematician who discovered the 18th known Mersenne prime in 1957. ('stɔkhɔlm is Sweden 's Capital and its largest City. It is the site of the national Swedish government, the parliament, and the "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. A mathematician is a person whose primary area of study and research is the field of Mathematics. In Mathematics, a Mersenne number is a positive integer that is one less than a Power of two: M_n=2^n-1 He also discovered the Riesel numbers. In Mathematics, a Riesel number is an Odd Natural number k for which the integers of the form k ·2 n −1 are He is currently at the Royal Institute of Technology. The Royal Institute of Technology or Kungliga Tekniska högskolan ( KTH) is a University in Stockholm, Sweden.