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.

Save guides, add subjects and pick up where you left off with your BBC account. The only even prime number is \({2}\). All other even numbers are divisible by \({2}\). The number \({1}\) ...