Alexis Lemaire used brain power alone to work out the answer to the 13th root of a random 200-digit number in 70.2 seconds at London's Science Museum.

The 27-year-old student correctly calculated an answer of 2,407,899,893,032,210, beating his record of 72.4 seconds, set in 2004.

The so-called 'mathlete' used a computer package to randomly generate a number before typing in the answer.

Mr Lemaire began demonstrating his mental calculation prowess by finding the 13th root of a random 100-digit number.

This feat soon became too easy for him and he abandoned trying to improve his time when he calculated an answer in less than four seconds in 2004.

In an attempt to sharpen his brain, Mr Lemaire trains daily for the considerably more difficult task of finding the 13th root of a random 200-digit number.

Lemaire broke the record in the Science Museum's History of Computing galley, where he had a backdrop of Charles Babbage's Difference Engine No.2, the world's first successful mechanical calculator, designed in the 1840s.

Jane Wess, curator of mathematics at the London Science Museum said: "He sat down and it was all very quiet - and all of a sudden he amazingly just cracked it.

"It's quite remarkable to see it happen. A very small number of people have this extraordinary ability.

"I believe that it is the highest sum calculated mentally."

RELATED ARTICLE: How to Memorize 10,000 Numbers or More