A 38-year-old with degrees in psychology, education and computer science needed only 11.8 seconds to calculate the 13th root of a 100-digit number in his head, setting a new record, organizers said.

Onlookers with electronic calculators needed more time to solve the problem that Gert Mittring figured on his own, with two umpires checking the time, at a math museum in the small German town of Giessen near Frankfurt in western Germany.

"I first think of an elegant problem-solving algorithm and the result comes immediately," said Mittring, who beat the previous record of 13.55 seconds, set by the Frenchman Alexis Lemaire in 2002, according to organizers of the Tuesday night event.

But his feat will not be immortalized in black and white in the Guinness Book of World Records, because the book no longer recognizes root calculations of random numbers due to the difficulty of standardizing the challenge, spokesman Sam Knight said Wednesday.

"Some numbers are easier to root than others — we are working on a way to standardize this," Knight said in a call from London.

"But that is not to take away from Mittring's performance. He is pretty incredible. He does hold the world record for memorizing 22 random digits in just four seconds."