Andrew Granville's Home Page

Selected expository articles

In the first, a Monthly note, we use Van der Waerden's Theorem and Fermat's Theorem on four squares in an arithmetic progression to give a crazy proof that there are infinitely many primes. In the second we first survey the many proofs, and then develop a dynamical systems approach. The third is survey of the other two for the LMS Newsletter.

  • Squares in arithmetic progressions and infinitely many primes
  • Using dynamical systems to prove that there are infinitely many primes
  • A panopoly of proofs that there are infinitely many primes
  • The infamous twin prime conjecture states that there are infinitely many pairs of distinct primes which differ by 2. In April 2013, Yitang Zhang proved the existence of a finite bound \( B \) such that there are infinitely many pairs of distinct primes which differ by no more than \( B \). Zhang even showed that one can take B = 70000000. In November 2013, inspired by Zhang's extraordinary breakthrough, James Maynard dramatically slashed this bound to 600, by a substantially easier method. Both Maynard and Terry Tao, who had independently developed the same idea, were able to extend their proofs to show that for any given integer \( m \geq 1\) there exists a bound \( B_m\) such that there are infinitely many intervals of length \( B_m\) containing at least \( m\) distinct primes. We prove this herein, even showing that one can take \( B_m=e^{8m+5}\). If Zhang's method is combined with the Maynard-Tao setup, then it appears that the bound can be further reduced to 246. This article introduces these results, and explain the arguments that allow them to prove their spectacular results. The second half develops a proof of Zhang's main novel contribution, an estimate for primes in relatively short arithmetic progressions.

    We explain the Bhargava composition algorithm for binary quadratic forms, in historical context

    As long as people have studied mathematics, they have wanted to know how many primes there are. Getting precise answers is a notoriously difficult problem, and the first suitable technique, due to Riemann, inspired an enormous amount of great mathematics, the techniques and insights permeating many different fields. In this article we will review some of the best techniques for counting primes, centering our discussion around Riemann's seminal paper. We will go on to discuss its limitations, and then recent efforts to replace Riemann's theory with one that is significantly simpler.

  • What is the best approach to counting primes?
  • Don't be seduced by the zeros!
  • Different approaches to the distribution of primes
  • An introduction to analytic number theory for Gowers' interesting mathematical writing project


    Prime number patterns (2009 Ford Prize)

    We develop various consequences of the Green-Tao theorem, for example showing that there exist polynomials of any given degree whose first \( k\) values are prime, and proving that there are magic squares of primes of arbitrary size.

    A survey about the AKS deterministic polynomial time primality test.


    Prime number races (2007 Ford Prize)

    This is a survey of what was then known about "prime number races". Subsequently two of my students from that time, Youness Lamzouri and Daniel Fiorilli, have proved several extraordinary results (some with collaborators) greatly extending this theory.


    It's as easy as abc (with Tom Tucker)

    A survey of the arithmetic consequences of the \( abc\)-conjecture.

    The number of odd entries in a row of Pascal's triangle is always a power of 2. These are either equally split between 1 and 3 mod 4, or are all 1 mod 4. Similarly, for every odd \( a\), the number of entries in a given row of Pascal's trinagle that are \( \equiv a \pmod 8\) is either 0 or a power of 2. We develop a theory to explain this.


    Recent research