Twin Primes

Twin primes are numbers wherein two numbers have a gap of two. According to Wikipedia, there are 808,675,888,577,436 twin prime pairs below 10^18, or 1 quintillion.
==Examples==
3 and 5 are twin primes
5 and 7 are twin primes
11 and 13 are twin primes, et al.
==Largest known twin prime==
3,756,801,695,685 · 2^666669 ± 1.
==See also==
*Cousin Primes, wherein the gap is four.
*Sexy Primes, wherein the gap is six.
Category:Types of Primes