Twin Primes

(3, 5), (5, 7), (11, 13), (17, 19), (29, 31)… twin primes, pairs of primes separated by exactly 2. Euclid proved there are infinitely many primes, but are there infinitely many TWIN primes? Two millennia have not answered it. Then in 2013, a virtually unknown mathematician, Yitang Zhang, proved that some bounded gap occurs infinitely often — a result no one expected, and the biggest breakthrough on the problem in a century.