Prime numbers have captivated mathematicians for ... but you still can’t find any primes,” explains study co-author Kevin Ford, a mathematician at the University of Illinois at Urbana-Champaign.

Apart from 2 and 5, all prime numbers end in 1, 3, 7 or 9 – they have to, else they would be divisible by 2 or 5 – and each of the four endings is equally likely.