The reason for the use of this term is that because a prime quadruple

is a group of four primes of the form p + i, where i = 0, 2, 6, 8, it

can only occur one every thirty numbers because in between there are

always four numbers (p + 11, p + 17, p + 23 and p + 29) that are

divisible by 3 and hence can never be prime.