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The following shows the beginning of the list of prime numbers: 2 , 3 , 5 , 7 , 11 , 13 , 17 , 19 , 23 , 29 . 2,3,5,7,11,13,17,19,23,29\ldots. The differences between two neighboring primes are 1 , 2 , 4 , 6 , 1,2,4,6, and possibly larger.

Is it possible to find two adjacent primes whose difference is at least 2018?

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1 solution

Jordan Cahn
Oct 22, 2018

The topic of prime gaps is well-studied.

For this problem, for any number n n , set consider the sequence n ! + 2 , n ! + 3 , , n ! + n n!+2, n!+3, \ldots, n!+n . The first term in the sequence is divisible by 2 2 , since 2 n ! 2\mid n! and 2 2 2 \mid 2 . Similarly, the second term in the sequence is divisible by 3 3 , and so on (with the k k th term divisible by k + 1 k+1 ) until we reach the last term, which must be divisible by n n . Thus, none of the numbers in our sequence can be prime, so these numbers belong to a gap of at least n 1 n-1 between two primes. So there must two consecutive primes that are separated by at least distance d d , for any value of d d .

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