Keep going with the other primes (7, 11, 13 etc), removing all the multiples of these as you go. You should end up with a list of 25 prime numbers between 1 and 100. These are shown in the grid below.

“That’s why I’m enthusiastic about this type of prime number.” Whether there are other memorable primes is not yet known. Mathematicians have checked all cases up to n = 60,000; apart from ...