Willem Klein

Origins and early life

Willem Klein, known as Wim Klein, was born in Amsterdam on 4 December 1912 to two Jewish parents, his father Henry Klein, a general practitioner, and his mother Emma Cohen, and no conversion is recorded; his Jewish family made him a target under the German occupation.

Work and career

He and his brother Leo, also a calculating prodigy, discovered as children that they could hold and manipulate enormous numbers in their heads. He began medical studies at his father's wish but abandoned them, and during the occupation he survived in hiding in the Netherlands while much of his family was murdered. After the war he made a living as a fairground and variety-hall performer under the stage names Pascal and Willy Wortel, multiplying long numbers and extracting roots in front of audiences.

In 1952 the mathematical centre in Amsterdam hired him, and from 1958 to 1976 he worked at CERN in Geneva, where physicists brought him calculations to check and where he was faster than the early computers for many problems, before the machines outran him and he was moved on to demonstrations. He set world records for mental arithmetic, taking the seventy-third root of a five-hundred-digit number in about two and a half minutes in 1976, and he memorised logarithm tables and the factorisations of thousands of numbers. He was murdered at his home in Amsterdam on 1 August 1986, in a crime that has never been solved.