The biggest prime number ever discovered is 17 million decimal digits long. Previously, the biggest prime number was 12 million digits long. It’s a lot of digits, but there is also a big gap between those two. Potentially there are a lot of “lost primes” waiting to be discovered. That’s what the Prime Challenge is about: using cloud computing to find the lost primes.


Prime numbers, defined as those that have no factors besides one and themselves, are at the heart of arithmetic and have numerous functional applications in today’s digital world, most notably public key cryptography. The aim of the Microsoft Windows Azure Prime Challenge is to provide a unique opportunity for users from all backgrounds: businesses, schools, universities, clubs or individuals to join the search for more prime numbers.

The challenge is open to all; everyone is encouraged to try and find a “lost prime.” To enter the challenge just go to and follow the instructions online.

The identification of new prime numbers is increasingly challenging, but possible for anyone. Forty per cent of the numbers between one and ten are prime but, as we progress up the number line, they taper off and become sparser. But in reality, as we get much further up the number line, nobody really knows as nobody has ever searched for them all.

In order to map large prime numbers of thousands of digits, powerful technology, which can quickly sift through and crunch numbers, is required. The purpose of the Prime Challenge is to give individuals, organisations, universities and schools the opportunity to access the computing power of our Windows Azure Datacentres to find and claim new prime numbers.

Prime numbers play a very important part in today’s business world, as they are used in the keys of public-key cryptography algorithms. It’s these algorithms that are used to secure most online data transfers, including email encryption and, most notably, bank card security through the SSL protocol. So nearly all online purchases that are made will use prime numbers in their security process.

The focus of the Prime Challenge is to find the “lost primes”; those prime numbers that have remained undiscovered in the race to always find the biggest prime. As the search for prime numbers has grown, mathematicians have always looked as far ahead as possible to find the next biggest prime, leaving plenty of unexplored territory within the number space. The Sieve of Eratosthenes, an ancient mathematical technique to identify prime numbers, dating back to the third century BC, is a simple algorithm that can be used to find prime numbers which also demonstrates that there is an infinite quantity of prime numbers.

The Microsoft Windows Azure Prime Challenge, will run until the 29th March (2903). To participate in the challenge, users will need to visit and follow the steps online. To assist with the search all participants can subscribe to a free Microsoft Windows Azure trial subscription giving them up to $200 of free access to create and run virtual machines.