"One proof of the existence of infinitely many twin primes involves assuming the opposite and reaching a contradiction.

Suppose there are only finitely many twin primes, say (p1, p1 + 2), (p2, p2 + 2), ..., (pn, pn + 2). Then consider the number N = (2 * pn + 3)^2 + 1. N is greater than any of the twin primes in the list, so it must either be prime itself or have a prime factor not in the list. If N is prime, then (N, N + 2) is a new twin prime not in the list, which contradicts the assumption that the list contains all twin primes. If N is not prime, then it must have a prime factor not in the list, say q. Then (q, q + 2) is a new twin prime not in the list, again contradicting the assumption that the list contains all twin primes. Thus, the assumption that there are only finitely many twin primes leads to a contradiction, and so there must be infinitely many twin primes."