At first glance there wasn’t, certainly nothing obvious. And yet, then again, there was something there, right in front of your eyes: as you kept on counting, you found more primes. There was no last prime, Euclid had proved as much twenty-three hundred years ago. “The primes are the raw material out of which we have to build arithmetic,” Hardy would write, “and Euclid’s theorem assures us that we have plenty of material for the task”; just as you never run out of numbers, you never run out of primes.
