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Friday, January 22, 2016

Prime numbers, as most of us remember from math class, are numbers greater than 1 that aren’t divisible by anything other than the number 1 and themselves. For example, 2, 3, 5, 7, 11 and 13 are the first six prime numbers. But as the numbers get larger, there are fewer and fewer of them.

Now there’s another prime number to add to the list: 2^{74,207,281} − 1. It has 22,338,618 digits and was discovered by a University of Central Missouri computer. The number is the new darling of the mathematical world.

“Everyone views mathematics as a subject that’s kind of done, but it’s great in math when something like this – we find a new prime number – and everyone gets very excited,” **Matt Parker**, a mathematician at Queen Mary University of London and a stand-up math comic, told *Here & Now’*s Jeremy Hobson.

*Correction: The audio for this interview incorrectly states that the number 1 is a prime number. The text above has been corrected. We regret the error. *

**What makes prime numbers special**

“The reason mathematicians love prime numbers is that they are described as the building blocks of other numbers, and so every other number can be written as some prime numbers multiplied together, but a prime number can’t be written as other numbers multiplied together and so they are as simple as you go when you look at multiplication to get numbers. If you want an insight into a number, you look at its prime factors and mathematicians love them because they allow them to understand and investigate all other numbers.”

**Why mathematicians search for bigger and bigger prime numbers**

“It’s the mathematical equivalent of climbing Everest. We do it because it’s a challenge and we do it because no one’s done it before.”

“These ridiculously big numbers are found purely for the sake of it. And so numbers that aren’t quite this ridiculously big, so otherwise very large prime numbers, are used for things like Internet inscription and modern online security relies on prime numbers and on the properties and theories behind them. But for ones like these that are just ridiculously large, it’s the mathematical equivalent of climbing Everest. We do it because it’s a challenge and we do it because no one’s done it before.”

**How long it would take to read out the record-breaking prime**

“I worked out, if you wanted to read it out, a digit a second, it would take about 250 days.”

**How the number was found**

“I spoke to Professor Curtis Cooper, he’s at the University of Central Missouri. This is his fourth record-breaking prime number, so I’m incredibly jealous. His secret is that he has managed to put software that searches for prime numbers on 800 of the computers across the University of Central Missouri and they are all around the clock looking for prime numbers. And fascinatingly, it actually found this prime number last September, on the 17th of September last year, but there was an error when it was reported back to the central server and no one knew. It was only when they were doing routine maintenance they were just checking the database earlier this month and they went, ‘What’s this, there’s a prime number here!’ And so the world record prime had sat there and the notification email hadn’t been automatically sent.”

**Matt Parker**, mathematician at Queen Mary University in London, stand-up math comic and author of the book “Things to Make and Do in the Fourth Dimension.” He tweets @standupmaths.

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