纪录片: Counting from Infinity
3000 years ago Euclid proved infinity of Prime numbers, but conjectured also infinity of twin primes :
(3,5), (5,7), (11,13)….
Some with gap of ‘4’ ( Cousin primes)
(7,11), (19,23) , (29,31)…
Gap of ‘6’ (Sexy Primes):
(23, 29)
The Twin Prime gaps (2,4,6 …) are bounded by max. 70,000, (min.2.)
Terence Tao mobilised the Internet community ‘Polymath Project’, using Zhang’s Sieve Method, reduce 70,000 to (hopefully) 16.
Chinese Tuition Singapore 
Typo correction:
Zhang’s bounded gap is 70,000,000 (70 million), it was the first maximum upper bound, could be further reduced using his technique.