Wim Klein: The Man Who Knew Every Number Personally
"Numbers are friends for me, more or less," he told Oliver Sacks, who preserved the line in his 1985 essay "The Twins." "It doesn't mean the same for you, does it, 3,844? For you it's just a three and an eight and a four and a four. But I say, 'Hi, 62 squared!'" That was Wim Klein's whole relationship to arithmetic in three sentences: not calculation but recognition, the way you spot a face in a crowd. For eighteen years CERN paid him to do it, until the machines caught up.
The Son of a Doctor
Willem Klein was born in Amsterdam on 4 December 1912 to Jewish parents — Henry Klein, a physician, and Emma Cohen. His childhood was difficult, largely because his father pressed him toward medicine when his talent and his interest lay entirely in mathematics. His mother killed herself in 1929, when he was sixteen.
He was not the only prodigy in the house. His older brother Leo possessed comparable calculating powers, and the two of them became a case study for the neurologist Stokvis, who drew a distinction that has stuck: Wim was an *auditory* calculator, Leo a *visual* one. Wim worked in sound — he heard numbers, muttered them, computed by ear. Leo saw them. Two brothers with the same rare gift, arriving at it through different senses.
Klein enrolled at the University of Amsterdam to read medicine in 1932, obeying his father, and took his bachelor's degree in 1935. He never finished the doctorate he began in 1941. It was also at university that he recognised his homosexuality — a fact that, in the Netherlands of the 1930s, added another layer of concealment to a life that would soon require a great deal of it.
Hiding
When the Germans invaded in 1940, Klein went to work in a Jewish hospital. In 1942 he went into hiding. He survived. Leo — the visual calculator, the brother whose mind was the twin of his own — was captured and murdered at the Sobibór extermination camp.
It is impossible to read the rest of Klein's life without that sentence sitting underneath it: the performing, the stage names, the circus tents, the restless movement between countries.
Twenty questions, eight minutes on the clock, and a percentile measured against everyone who has taken it. No sign-up.
Take the IQ test →The Circus Years
From 1945 to 1952 Klein made his living as a performer, touring France, Belgium and the Netherlands with circuses under the stage name Pascal. The act was arithmetic. Audiences shouted numbers; he multiplied them, extracted their roots, named their factors, faster than anyone in the tent could check.
Then, in 1952, the Mathematisch Centrum in Amsterdam hired him as a scientific calculator. The job title is now archaic and needs explaining: before electronic computers were widely available, "computer" and "calculator" were job descriptions held by human beings. Research institutions employed people to grind through the arithmetic that theory demanded. Klein, who had been doing it for laughs in a circus, was suddenly doing it for physics.
CERN, and the Machines
In 1958 he moved to CERN, the European particle physics laboratory in Geneva, where he stayed for eighteen years. For a period he was genuinely useful: a physicist with a messy integral or a chain of multiplications could walk down the corridor and get an answer faster than any device on the premises would produce one.
Then the devices got better. By the 1960s Klein felt himself being reduced to a mascot, wheeled out to astonish visitors while the actual computation migrated to machines that never tired, never erred and never asked for a salary. It is one of the sadder occupational obsolescences of the twentieth century, and Klein lived it consciously, in a building full of the people who were engineering it. He took early retirement in 1976, homesick for the Netherlands.
The 73rd Root
Retirement freed him to chase records. Performing now as Willy Wortel, he turned to the kind of feats that could be certified rather than merely applauded. On 27 August 1976 he extracted the 73rd root of a 500-digit number in 2 minutes 43 seconds, and the Guinness Book of Records took it down.
The feat deserves unpacking, because its difficulty is not obvious. A 500-digit number cannot be held in ordinary working memory, let alone manipulated in it. The answer — the number which, multiplied by itself seventy-three times, produces that 500-digit figure — has to be built digit by digit through successive approximation, with each step requiring exact arithmetic on quantities that would fill several lines of a page. Klein did it in less than three minutes, aloud, in his head.
An Unsolved Death
On 1 August 1986, Klein was murdered in his Amsterdam home, stabbed with a knife. A suspect was arrested and released for insufficient evidence. The case has never been solved.
Why Wim Is Called a Genius
The honest framing is that Klein's gift was extraordinarily narrow and extraordinarily deep. He did not prove theorems, did not advance mathematics, and never completed the doctorate he started. What he possessed was a kind of numerical perception: an internalised, instantly accessible map of the multiplicative structure of the integers. When he greeted 3,844 as "62 squared," he was not deducing it — he was recognising it, the way a musician hears a chord rather than three separate pitches. Coupled to this was an auditory working memory of freakish capacity, capable of holding and manipulating hundreds of digits without external notation.
The neurological interest was real, and formally documented: Stokvis studied both Klein brothers and classified their differing modes, and Oliver Sacks thought Klein's self-description important enough to quote in his essay "The Twins." That quotation remains one of the most cited windows into what such a mind feels like from the inside.
The counter-case is substantial and Klein's own career makes it. Mental calculation is not mathematics; it is a specialised skill that, however astonishing, was fully and permanently superseded by inexpensive machines within his working lifetime. Everything Klein could do in 163 seconds, a pocket calculator would do instantly and a computer would do a billion times over. He produced no original result that survives him. And his relegation at CERN to the role of visitor attraction was a verdict, delivered by the institution best qualified to deliver it, on the practical value of the skill. What remains is not utility but evidence — a demonstration of how strange and how capacious a human mind can be at one specific thing.
Legacy
Klein occupies a category that closed behind him. He was among the last people to hold a paying job as a human calculator at a serious scientific institution, and he watched that job be abolished by the machines being built around him. What he leaves is a line about numbers being friends, quoted by Sacks and repeated ever since by anyone trying to explain what prodigious calculators actually experience; a Guinness record extracted from a 500-digit number; and a case study in what happens when a mind is perfectly adapted to a task the world stops needing.
