The primes contain arbitrarily long arithmetic progressions

You need to know: Prime numbers.

Background: A (non-trivial) arithmetic progression of length n is a sequence a_1, a_2, \dots, a_n of real numbers such that a_i = a_1 + (i-1)d, \, i=1,2,\dots,n for some d\neq 0.

The Theorem: On 8th April 2004, Ben Green and Terence Tao submitted to arxiv a paper in which they proved that for every positive integer n there exist an arithmetic progression of length n consisting of only prime numbers.

Short context: In 1939, Van der Corput proved that the set of primes contains infinitely many arithmetic progressions of length n=3. The Theorem proves this for all n. Before 2004, this was open even for n=4. Moreover, Green and Tao proved that even any positive proportion of primes contains infinitely many arithmetic progressions of length n for all n. This generalises an earlier theorem of Green, which proves this for n=3.

Links: Free arxiv version of the original paper is here, journal version is here. See also Section 8.2 of this book for an accessible description of the Theorem.

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