Man gets 13th root in 49 minutes
A 24-year-old French student claimed a world record after he became the first person to figure out the 13th root of a 200-digit number by mental arithmetic alone.
Alexis Lemaire, who is studying for a master's degree in computer studies at the University of Reims, eastern France, took 48 minutes and 51 seconds to arrive at the 16-figure answer.
The competition was overseen by a mathematician and a public bailiff to ensure that the answer was right and Lemaire had only used his own brainpower to get there. Use of a computer, calculator and even a pencil and paper were not allowed.
In December, Lemaire set a world speed record of 3.625 seconds for finding the 13th root of a 100-digit number. The previous record of 11.8 seconds had been held by a 38-year-old German, Gert Mittring.
The 100-digit record used to feature in the Guinness Book of Records, but was axed in 2002.
Lemaire described the 200-digit task as "the most difficult challenge in mental arithmetic in history," as there were a potential 400,000 billion permutations in the answer.
He said his calculation method would be published next month in the French magazine Sciences et Avenir (Science and Future), which hosted the event.
The 13th root is a number that must be multiplied by itself 13 times in order to equal a given value.
The student, who is learning 40 languages simultaneously in his spare time, has promised to reveal part of his technique. Would-be challengers are directed to the website http://www.13throot.com