Difference between revisions of "Twin prime"
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| − | Two primes that differ by exactly 2 are known as | + | Two primes that differ by exactly 2 are known as '''twin primes'''. The following are the smallest examples:<br> |
3, 5<br> | 3, 5<br> | ||
5, 7<br> | 5, 7<br> | ||
Revision as of 23:53, 19 June 2006
Two primes that differ by exactly 2 are known as twin primes. The following are the smallest examples:
3, 5
5, 7
11, 13
17, 19
29, 31
41, 43
It is not known whether or not there are infinitely many pairs of twin primes. A natural attempt to prove that there are infinitely many twin primes is to consider the sum of reciprocals of all the twin primes 
. If 
, then there would be infinitely many twin primes. However, it turns out that 
, which proves nothing. The number B is called Brun's constant.
