<h2>Twin primes</h2>

A <a href="http://en.wikipedia.org/wiki/Twin_prime" target="_blank">twin prime</a> is a pair of prime numbers with the smaller prime separated by 2 from the larger. The first twin primes are <i>(3,5)</i>, <i>(5,7)</i>, and <i>(11,13)</i>.
It is still not known whether there are infinitely many twin primes. This question is one of the great <a href="http://en.wikipedia.org/wiki/List_of_unsolved_problems_in_mathematics" target="_blank">unsolved problems of mathematics</a>.
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