Hans Ivar Riesel (May 28, 1929 in
Stockholm – December 21, 2014) was a
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
mathematician
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems.
Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change.
History
On ...
who discovered the 18th known
Mersenne prime
In mathematics, a Mersenne prime is a prime number that is one less than a power of two. That is, it is a prime number of the form for some integer . They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th ...
in 1957, using the computer
BESK
BESK (''Binär Elektronisk SekvensKalkylator'', Swedish for "Binary Electronic Sequence Calculator") was Sweden's first electronic computer, using vacuum tubes instead of relays. It was developed by '' Matematikmaskinnämnden'' ( Swedish Boar ...
: this prime is 2
3217-1 and consists of 969 digits. He held the record for the largest known prime from 1957 to 1961, when Alexander Hurwitz discovered a larger one. Riesel also discovered the
Riesel number In mathematics, a Riesel number is an odd natural number ''k'' for which k\times2^n-1 is composite for all natural numbers ''n'' . In other words, when ''k'' is a Riesel number, all members of the following set are composite:
:\left\.
If the for ...
s as well as developing the
Lucas–Lehmer–Riesel test
In mathematics, the Lucas–Lehmer–Riesel test is a primality test for numbers of the form ''N'' = ''k'' ⋅ 2''n'' − 1 ( Riesel numbers) with odd ''k'' < 2''n''. The test was developed by Hans ...
. After having worked at the
Swedish Board for Computing Machinery The Swedish Board for Computing Machinery ( sv, Matematikmaskinnämnden, MMN) was a Swedish government agency which built Sweden's first computers: BARK and BESK.
A governmental study into the need for computing machinery in Sweden had been conduct ...
, he was awarded his
Ph.D.
A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: or ') is the most common degree at the highest academic level awarded following a course of study. PhDs are awarded for programs across the whole breadth of academic fields. Because it is ...
from
Stockholm University in 1969 for his thesis ''Contributions to numerical number theory'',
LIBRIS
LIBRIS (Library Information System) is a Swedish national union catalogue maintained by the National Library of Sweden in Stockholm
Stockholm () is the capital and largest city of Sweden as well as the largest urban area in Scandinavia ...
br>1768091
/ref> and in the same year joined the Royal Institute of Technology as a senior lecturer and associate professor.
Selected publications
*
See also
* Riesel number In mathematics, a Riesel number is an odd natural number ''k'' for which k\times2^n-1 is composite for all natural numbers ''n'' . In other words, when ''k'' is a Riesel number, all members of the following set are composite:
:\left\.
If the for ...
* Riesel Sieve
Riesel Sieve was a volunteer computing project, running in part on the BOINC platform. Its aim was to prove that 509,203 is the smallest Riesel number, by finding a prime of the form for all odd smaller than 509,203.
Progress
At the start of t ...
References
External links
Riesel's web pageObituary
1929 births
2014 deaths
Number theorists
KTH Royal Institute of Technology faculty
Swedish mathematicians
{{Sweden-mathematician-stub