A mathematical term which refers to a pair of prime numbers whose difference is 6 (The prefix sex- comes from the Latin for six). The smallest pair of sexy primes is 5 and 11.
There are also sexy prime triplets and quadruplets that follow the same idea. However, they have the added requirement that the next number in their sequence not be prime. For example, the triplet 5, 11, 17 is not a sexy prime triplet because 23 is also prime (as is 29, forming the only possible sexy quintuplet). However, the set 7, 13, 19 qualifies as a sexy triplet since 25 is a composite number.
Sexy primes are a cousin of twin primes; therefore, theoretically, there should be an infinite number of sexy prime pairs. However, the twin prime conjecture remains an open question in number theory.