German Discovers Longest Prime Number

A German eye specialist with a keen amateur interest in mathematics has discovered the world's largest prime number after a 50-day search using his personal computer.

Dr Martin Nowak, who has his own practice in the south German town of Michelfeld, stumbled upon the number last week, breaking the previous record for a prime number by half a million digits.

Prime numbers are divisible only by themselves and 1. While the first prime numbers 2, 3, 5, and 7, are easy to identify, Dr Nowak's monster prime number is more than 7.8m digits long and is written as 2 to the 25,964,951st power minus 1.

The number belongs to a special class of rare prime numbers known as Mersenne primes, named after a 17th century French monk who first studied them 350 years ago. So far only 42 have been found.

Yesterday Dr Nowak was reluctant to talk about his discovery, made using a special programme on his 2.4GHz Pentium 4 computer. "He's busy. He has a full afternoon seeing patients. He's doesn't want to comment," a spokeswoman at Dr Nowak's clinic said.

The eye surgeon is one of thousands of volunteers using software provided by the Great Internet Mersenne Prime Search (Gimps), a project to discover the holy grail of prime number research - a 10m-digit prime number. It took experts five days to work out that Dr Nowak's new number was indeed bigger than the previous biggest prime, discovered last May by an American. His number has 7,816,230 digits.