What finite gap bound did Yitang Zhang prove exists infinitely often between prime numbers in 2013?

Answer

70 million

In 2013, Zhang proved that there are infinitely many pairs of prime numbers separated by a gap of no more than 70 million. This demonstrated that prime gaps are bounded, even if the initial bound was large.

What finite gap bound did Yitang Zhang prove exists infinitely often between prime numbers in 2013?
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