Largest known prime number discovered in Missouri

The prime was discovered by a US mathematician using a computer programme

. (REX Features)

The largest known prime number has been found by a computer programme at a US university.

Prime numbers can only be divided by themselves and one, and are vital for computer encryption.

The new number - written as 2^74,207,281-1 - is more than 22 million digits long and was published by Dr Curtis Cooper at the University of Central Missouri.

The discovery was part of the Great Internet Mersenne Prime Search (Gimps) programme to find new prime numbers.

The number is five million longer than the previous largest prime found in 2013 which was also discovered by Dr Cooper using the computer software.

Prime numbers are used by online banking, shopping private message services as encryption keys to protect data.

The new prime is currently too long to be of any practical use as the prime numbers currently used are typically hundreds of digits long not millions - but it has potential to be useful in the future.

In a statement, Gimps said: “The prime number, also known as M74207281, is calculated by multiplying together 74,207,281 twos then subtracting one. It has 22,338,618 digits -- almost 5 million digits longer than the previous record prime number.

“While prime numbers are important for cryptography, this prime is too large to currently be of practical value.”

The Gimps project - named after 17th century French monk Marin Mersenne who studied primes - was founded in 1996 and has so far discovered 15 numbers.