Shakuntala Devi, also known as the human computer, gave the 23rd root of a 201 digit number in 50 seconds. The answer was verified at the US Bureau of Standards by the UNIVAC 1101 computer, for which a special program had to be written to perform such a large calculation.
Devi traveled to several countries around the world demonstrating her arithmetic talents. She was on a tour of Europe throughout 1950 and was in New York City in 1976.
In 1988, she traveled to the US to have her abilities studied by Arthur Jensen, a professor of educational psychology at the University of California, Berkeley. Jensen tested her performance at several tasks, including the calculation of large numbers. Examples of the problems presented to Devi included calculating the cube root of 61,629,875 and the seventh root of 170,859,375. Jensen reported that Devi provided the solution to the above mentioned problems (395 and 15, respectively) before Jensen could copy them down in his notebook.
On 18 June 1980, she demonstrated the multiplication of two 13-digit numbers – 7,686,369,774,870 × 2,465,099,745,779. These numbers were picked at random by the Department of Computing at Imperial College London. She correctly answered 18,947,668,177,995,426,462,773,730 in 28 seconds. This event was recorded in the 1982 Guinness Book of World Records.
Shakuntala Devi explained many of the methods she used to do mental calculations in her book Figuring: The Joy of Numbers.