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Figure out this prime and win pound;50,000

With the exam season under way, most schools probably think they have enough on their plate without joining the search for a number so long it would take nearly two months to read aloud.

But those who take the time to help to look for the world's longest prime number may find it worth their while, according to Marcus du Sautoy, Oxford university professor of maths.

In The TES today, he urges schools to join the unfortunately- titled Gimps (Great Internet Mersenne Prime Search) which uses the processing power of idle computers to search for ever-larger primes.

"One shouldn't underestimate the potential of the Gimps to draw students into deeper questions of mathematics," he says.

"But if that weren't incentive enough, then perhaps the lure of financial gain might help. A prize of 100,000 dollars (pound;53,118) awaits the first person to find a prime with more than 10 million digits.

"Getting a school's computers joining the hunt for the next record prime might just help solve all those financial problems."

Prime numbers have a special place in maths as they cannot be divided by any smaller number except one.

There is an infinite number of primes, but the largest known is 7.8 million digits long. It would take about six weeks to read the number out loud and it was discovered by a doctor in Germany who had 24 computers taking part in the Gimps.

Until 1951, the largest known prime number was 39 digits. But the advent of electronic computers pushed this up to almost 1,000 by the start of the 1960s and more than 200,000 by the early 1990s.

But why search for ever-larger primes? A website dedicated to primes puts it down to humans' competitive instinct. It said: "Those who found them are like the athletes in that they outran their competition. They are like the mountain climbers in that they have scaled new heights. Their greatest contribution to mankind is not merely pragmatic, it is to the curiosity and spirit of man."

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The Great Internet Mersenne Prime Search

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