The number certainly doesn't seem particularly exciting. It's not a prime number or a power of 2 or the square of some other number. The digits don't seem to follow any obvious pattern.

Prime numbers have captivated mathematicians for thousands of years—and now cloud computing is helping them chase the biggest ones yet.

The smallest such number is 561: For any integer b, b561 – b is always a multiple of 561, even though 561 is not prime.

Number theorist Yitang Zhang tackled a problem that could tame the randomness of prime numbers. Credit: George Csicsery/Zala Films A mathematician who went from obscurity to luminary status in ...