Twin primes are
prime numbers which differ by exactly 2. The twin
prime conjecture states that there are infinitely many twin primes—that is, there are infinitely many pairs of prime numbers (p, q), where p < q, such that q − p = 2.
The first few twin primes are (3, 5), (5, 7), (11,
13), (17, 19), (29, 31), (41, 43), ...