# Kevin Ford's Papers

### Research Papers

1. Some infinite series identities . Kevin Ford
Proc. of the Amer. Math. Soc. 119 (1993), no. 3, 1019-1020.
Small errata: Must add the hypothesis d≠ 1, d≠ -1.

2. The representation on numbers as sums of unlike powers. Kevin Ford
J. London Math. Soc. (2) 51 (1995), 14-26.
3. The representation on numbers as sums of unlike powers, II . Kevin Ford
J. Amer. Math. Soc. 9 (1996), 919-940.
Addendum and Corrigendum , J. American Math. Soc. 12 (1999), 1213.

4. New estimates for mean values of Weyl sums . Kevin Ford
International Mathematical Research Notices 1995, 155-171.
Abstract: We invent a new method for extracting more efficiently a bound on the 2s-moment of a degree-k Weyl sum using bounds on Vinogradov's Mean Value. Consequences include large improvements in the known range of validity of the asymptotic formula in Waring's problem. (Note: in 2015, the Main Conjecture for Vinogradov's Mean Value was solved in the full range of parameters by Bourgain, Demeter and Guth, and consequently the methods of this paper appear now to be obsolete)

5. Sums and products from a finite set of real numbers . Kevin Ford
The Ramanujan Journal 2, no. 1-2, (1998), 59-66. Reprinted in Analytic and elementary number theory: A tribute to mathematical legend Paul Erdős , (K. Alladi, P. D. T. A. Elliott, A. Granville and G. Tenenbaum, eds.), Springer, 1998.

6. The distribution of totients . Kevin Ford
Note: the PDF version here is the updated 2012 version, with various corrections and simplifications to the original paper.
The Ramanujan Journal 2, no. 1-2. (1998), 67-151. Reprinted in Analytic and elementary number theory: A tribute to mathematical legend Paul Erdős , (K. Alladi, P. D. T. A. Elliott, A. Granville and G. Tenenbaum, eds.), Springer, 1998.
Abstract: A totient is a number in the image of Euler's function φ(n). This paper is a comprehensive investigation of the set of totients, solving a number of long-standing open problems. The primary result is a determination of the precise order of growth of V(x), the number of totients which are at most x. This follows earlier works on the problem going back to 1929 by Pillai, Erdős, Hall, Pomerance and the most recent work of Maier and Pomerance (1988). The formula is rather complex to write down. The proof reveals fine detail about the normal multiplicative structure of a typical totient. We also study A(m), the number of solutions of φ(n)=m, and Vk(x), the number of integers m≤x for which A(m)=k. We show that for every k, either Vk(x) is identically zero or Vk(x) has the same order or growth as V(x), i.e., a positive proportion of totients have multiplicity k (in fact the latter occurs for k>1; see papers No. 7 and 10 below). Moreover, the same results hold if φ is replaced by another multiplicative function which has 'similar' behavior at primes, such as the sum of divisors function σ(n). Finally, we study the Carmichael Conjecture (dating to 1907) which states that A(m)=1 cannot hold for any m. Making use of a large-scale computation, we show that it is true for m<101010.

7. On two conjecture of Sierpinski concerning the arithmetic functions σ and φ , Kevin Ford and Sergei Konyagin.
In the book Number Theory in Progress (Zakopane, Poland 1997; Kálmán Györy, Henryk Iwaniec, Jerzy Urbanowicz, eds), de Gruyter (1999), 795-803.
Abstract: Around 1955, W. Sierpiński conjectured that for any positive integer k, there is a number m so that the equation σ(x)=m has exactly k solutions x. Here σ(x) is the sum of the positive divisors of x. In this paper, the conjecture is proved. Sierpiński also conjectured that for every k>1, there is a number m so that the equation φ(x)=m has exactly k solutions x, where φ is Euler's 'totient' function. This conjecture is proved for all even values of k. The proof includes a novel combinatorial device, plus a sieve whose desired output is products of more than one prime (as opposed to prime numbers themselves). See also the companion paper No. 10 below.

8. Residue classes free of values of Euler's function , Kevin Ford, Sergei Konyagin and Carl Pomerance.
In the book Number Theory in Progress (Zakopane, Poland 1997; Kálmán Györy, Henryk Iwaniec, Jerzy Urbanowicz, eds), de Gruyter (1999), 805-812.

9. The normal behavior of the Smarandache function , Kevin Ford
Smarandache Notions J. 10, no. 1-2-3. (1999), 81-86.
Note: This manuscript was neither submitted to, nor refereed by, this journal. It was, however, reviewed by Math Reviews.
ERRATA: The constants appearing in Theorem 1 and Corollary 3 are incorrect. The factors 1+log 2 should be replaced by 2. The main error is on page 4, equation (2). The second argument to the second ψ term should be p, not q (Thanks to A. Ivić for discovering this).

10. The number of solutions of φ(x)=m , Kevin Ford
Annals of Math. 150 (1999), 283-311.
Abstract: Around 1955, W. Sierpiński conjectured that for any positive integer k>1, there is a number m so that the equation φ(x)=m has exactly k solutions x, where φ is Euler's 'totient' function. This conjecture was proved for all even values of k by the author and Konyagin (see paper No. 7 above). In this paper, the conjecture is proved for every k by a different method. The proof uses induction, using a known integer m with A(m)=k to construct a number m' with A(m')=k+2 (it is similar to a method introduced in paper No. 6 above). One of the main tools is the famous theorem of Chen, used in the following form: for each fixed, even positive integer m, there are at least cx/(log x)2 primes p≤x so that (p-1)/m is prime or the product of two primes.

11. The Brun-Hooley sieve , Kevin Ford and Heini Halberstam.
J. Number Theory 81 (2000), 335-350.

12. Waring's problem with polynomial summands . Kevin Ford
J. London Math. Soc. (2) 61 (2000), 671-680.

13. On an irreducibility theorem of A. Schinzel associated with coverings of the integers , Michael Filaseta, Kevin Ford and Sergei Konyagin
Illinois J. of Math. 44 (2000), 633-643.

14. Zeros of Dirichlet L-functions near the real axis and Chebyshev's bias , Carter Bays, Kevin Ford, Richard Hudson and Michael Rubinstein.
J. Number Theory 87 (2001), 54-76.

15. An explicit sieve bound and small values of σ(φ(m)) . Kevin Ford
Periodica Math. Hung. 43 (1-2), (2001), 15-29.

16. Sign changes in πq,a(x) - πq,b(x) , Kevin Ford and Richard Hudson
Acta Arithmetica 100 (2001), 297-314.

17. The prime number race and zeros of Dirichlet L-functions off the critical line , Kevin Ford and Sergei Konyagin
Duke Math. J. 113 (2002), 313-330.
Abstract: Let πq,a(x) denote the number of primes ≤x in the progression a modulo q. We study subtle inequities in these functions, with q fixed and variable a (sometimes called 'prime race problems'). It is known unconditionally for many triples (q,a,b) that the difference πq,a(x) - πq,b(x) changes sign infinitely often, although there may be a pronounced bias toward one sign (first observed by Chebyshev in 1853). Similar results for the comparison of three or more prime counting functions all require the assumption of ERH (extended Riemann Hypothesis for the Dirichlet L-functions modulo q). In this paper we show that the assumption of ERH is, in a sense, necessary. That is, we prove, for any quadruple (q,a,b,c) with a,b,c co-prime to q, that the existence of certain hypothetical configurations of zeros of Dirichlet L-functions lying off the critical line imply that one of the six possible orderings of the three functions πq,a(x), πq,b(x), πq,c(x) does not occur at all for large enough x.

18. Vinogradov's integral and bounds for the Riemann zeta function . Kevin Ford
Proc. London Math. Soc. 85 (2002), 565-633. List of errata .
Abstract: We give a new upper bound for the Riemann zeta function near the line ℜs=1. Specifically, we prove the bound |ζ(σ+it)| ≤ A|t|B(1-σ)3/2, with A=76.2 and B=4.45, valid for σ≥ 1/2 and |t|≥ 1. Previously, such a bound was known with B=18.8 (the value of B is far more important in applications). Applications include improvements to error terms in the divisor problems, and numerical improvements to zero-free regions for ζ(s); see paper No. 19 below. The main new ingredient is the utilization of multidimensional exponential sums over smooth numbers (numbers without large prime factors).

19. Zero-free regions for the Riemann zeta function . Kevin Ford
In the book Number Theory for the Millenium (Urbana, IL, 2000) (M. A. Bennett, B. C. Berndt, N. Boston, H. G. Diamond, A. J. Hildebrand and W. Phillip, eds), vol. II (2002), 25-56.

20. Maximal collections of intersecting arithmetic progressions . Kevin Ford
Combinatorica 23 (2) (2003), 263-281.

21. The jumping champions of the Farey series, Christian Cobeli, Kevin Ford and Alexandru Zaharescu
Acta Arithmetica 110 (2003), no. 4, 259-274

22. The prime number race and zeros of Dirichlet L-functions off the critical line, II. , Kevin Ford and Sergei Konyagin
Proceedings of the session in analytic number theory and Diophantine equations (Bonn, January-June 2002), Bonner Mathematische Schiften, Nr. 360 (D. R. Heath-Brown, B. Z. Moroz, editors), Bonn, Germany, 2003, 40 pages.

23. A strong form of a problem of R. L. Graham . Kevin Ford
Canadian Math. Bulletin 47 (3), (2004), 358-368.

24. On Bombieri's asymptotic sieve . Kevin Ford
Trans. Amer. Math. Soc. 357 (2005), 1663-1674.

25. Cycling via common divisors; Solution of Problem 11019(b), Kevin Ford and Sergei Konyagin
Amer. Math. Monthly 111 (2005), 277-278.
Notes: This file corrects a few typos in the published version.

26. On the distribution of imaginary parts of zeros of the Riemann zeta function , Kevin Ford and Alexandru Zaharescu
J. reine angew. Math. 579 (2005), 145-158.

27. On the maximal difference between an element and its inverse in residue rings . Kevin Ford, Mizan R. Khan, Igor E. Shparlinski and Christian L. Yankov
Proc. Amer. Math. Soc. 133 (2005), 3463-3468.

28. Values of the Euler function in various sequences William D. Banks, Kevin Ford, Florian Luca, Francesco Pappalardi and Igor E. Shparlinski,
Monatshefte Math. 146 (2005), 1-19.

29. Sieving by large integers, and covering systems of congruences , Michael Filaseta, Kevin Ford, Sergei Konyagin, Carl Pomerance and Gang Yu
J. Amer. Math. Soc. , 20 (2007), 495-517.
Abstract: A covering system is a finite set of congruence classes, say aj mod mj, 1≤j≤k, whose union is all the integers. Of particular interest are those covering systems with distinct moduli mj. The concept was invented by Erdős, who has a number of famous problems about them. In this paper, we prove a conjecture of Erdős and Ron Graham, that for any K>1, if N is sufficiently large then there does not exists a covering system with distinct moduli from the interval (N,KN]. We also prove a conjecture of Erdős and John Selfridge, that for any K>1, if N is sufficiently large then there does not exists a covering system with distinct moduli > N whose sum of reciprocals is less than K. In fact, in each of these theorems, the quantity K may grow as a function of N (almost linearly), and each modulus may be be repeated a small number of times (also slowly growing as a function of N). These are accomplished using new methods of bounding the density of the union of congruence classes, when the moduli are not pairwise coprime.

30. The distribution of integers with at least two divisors in a short interval , Kevin Ford and Gérald Tenenbaum
Quart. J. Math. Oxford 58 (2007), 187-201.

31. Generalized Smirnov statistics and the distribution of prime factors . Kevin Ford
Funct. Approx. Comm. Math. 37.1 (2007), 119-129.

32. Localized large sums of random variables , Kevin Ford and Gérald Tenenbaum
Stat. Prob. Letters 78 (2008), 84-89.

33. Sharp Probability estimates for generalized Smirnov statistics . Kevin Ford
Monatshefte Math. 153 (2008), 205-216.

34. The distribution of integers with a divisor in a given interval . Kevin Ford
Annals of Math. (2) 168 (2008), 367-433.
Abstract: This paper solves several central problems of Erdős about the distribution of divisors of integers. Let $$H(x,y,z)$$ denote the number of integers $$n\le x$$ that have a divisor between $$y$$ and $$z$$. The main theorem in this paper is a determination of the exact order of growth of $$H(x,y,z)$$ for all $$x,y,z$$. (that is, bounding $$H(x,y,z)$$ between two constant multiples of an explicit smooth function of $$x,y,z$$ ). This caps off a program begun by Besicovich in the 1930s, and earlier estimates of Erdős, Tenenbaum and others. In particular, in the important special case $$z=2y$$, $$H(x,y,2y)$$ has order $\frac{x}{(\log y)^{\lambda}(\log\log y)^{3/2}},$ uniformly for $$3\le y\le x^{1/2}$$, where $$\lambda = 1-(1+\log\log 2)/\log 2=0.086071332...$$

One application is the solution of the Erdős "multiplication table problem" (posed in 1955): let $$A(N)$$ be the number of distinct entries in an $$N$$ by $$N$$ multiplication table. Then $$A(N)$$ lies between two constant multiples of $\frac{N^2}{(\log N)^\lambda (\log\log N)^{3/2}}$ We also determine the order of $$H_r(x,y,z)$$, the number of integers $$n\le x$$ that have exactly $$r$$ divisors between $$y$$ and $$z$$, in a wide range of the parameters, including the central case $$z=2y$$. In this case, we show that for every $$r \ge 1$$, $$H_r(x,y,2y)$$ has the same order as $$H(x,y,2y)$$, disproving a 1960 conjecture of Erdős. A key tool in the proofs is a new avoidance bound for random walks.

The new bounds for random walks was generalized and strengthened in sequel papers devoted to random walk avoidance theory (nos. 31, 33, 42 in this list).

The techniques of this paper were also used to provide tight bounds on the probability that a random permutation on n letters has a fixed set of a given size: Permutations fixing a k-set (2016).

35. Integers with a divisor in (y,2y] . Kevin Ford
Anatomy of Integers (Jean-Marie De Koninck, Andrew Granville, and Florian Luca, eds), CRM Proc. and Lect. Notes 46 , Amer. Math. Soc., Providence, RI, 2008, 65-80. Updated, simplified version (2012)
Abstract: This is an alternative and simplified proof of a central case of the main theorem of paper No. 34 above, namely the determination of the order of growth of H(x,y,2y), the number of integers n≤x that have a divisor between y and 2y. This paper will be periodically updated, as I or others come up with simplifications.

36. Generalized Euler constants , Kevin Ford and Harold G. Diamond
Math. Proc. Cambridge Phil. Soc. 145 (2008), 27-41.

37. Divisors of the Euler and Carmichael functions, Kevin Ford and Yong Hu
Acta Arithmetica 133 (2008), 199-208.

38. On curves over finite fields with Jacobians of small exponent, Kevin Ford and Igor E. Shparlinski
Int. J. Number Theory 4 (2008), 819-826.

39. On the distribution of imaginary parts of zeros of the Riemann zeta function, II , Kevin Ford, K. Soundararajan and Alexandru Zaharescu
Math. Annalen 343 (2009), 487-505.

40. Diophantine approximation with arithmetic functions , Emre Alkan, Kevin Ford and Alexandru Zaharescu
Trans. Amer. Math. Soc. 361 (2009), 2263-2275.

41. On the largest prime factor of the Mersenne numbers , Kevin Ford, Florian Luca and Igor E. Shparlinski
Bull. Austr. Math. Soc. 79 (2009), 455-463.

42. Sharp probability estimates for random walks with barriers . Kevin Ford
Prob. Th. Rel. Fields 145 (2009), 269-283.

43. Diophantine approximation with arithmetic functions, II , Emre Alkan, Kevin Ford and Alexandru Zaharescu
Bull. London Math. Soc. 41 (2009), 676-682.

44. Common values of the arithmetic functions φ and σ , Kevin Ford, Florian Luca and Carl Pomerance
Bull. London Math. Soc. 42 (2010), 478-488.
 Abstract: Do the ranges of Euler's totient function $$\phi$$ and the sum-of-divisors function $$\sigma$$ have infinite intersection? In 1958, Erdős conjectured that they do. This follows trivially from either of two other famous conjectures, the twin prime conjecture (if $$p$$ and $$p+2$$ are both prime, then $$\phi(p+2)=p+1=\sigma(p)$$ and the conjecture that there are infinitely many Mersenne primes (if $$2^p-1$$ is prime, then $$\phi(2^{p+1}) = 2^p = \sigma(2^p-1)$$ . Both of these conjectures are out of reach. Numerical evidence indicates that intersections are plentiful, however, in fact below 107 about half of all numbers in the range of $$\phi$$ are also in the range of $$\sigma$$. In this paper, we prove Erdős conjecture unconditionally. One key tool is an upper bound for the number of constrained prime chains from paper No. 47 (below).

45. Geometric Properties of Points on Modular Hyperbolas , Kevin Ford, Mizan Khan and Igor Shparlinski
Proc. Amer. Math. Soc. 138 (2010), 4177-4185.

46. On the divisibility of Fermat quotients , Jean Bourgain, Kevin Ford, Sergei V. Konyagin and Igor E. Shparlinski
Michigan Math. J. 59 (2010), 313-328.

47. Prime chains and Pratt trees , Kevin Ford, Sergei V. Konyagin and Florian Luca
Geom. Funct. Anal. 20 (2010), 1231-1258.
Abstract: A prime chain is a sequence $$p_1, p_2, \ldots, p_k$$ of primes such that $$p_j | (p_{j+1}-1)$$ for each $$j\le k-1$$. We introduce a number of new methods for counting prime chains with various constraints, primarily with the length $$k$$ unconstrained. For example, the number of prime chains starting at a given prime $$p$$ and ending at a prime less than $$xp$$ is, for any $$\varepsilon>0$$, at most $$C(\varepsilon) x^{1+\varepsilon}$$ for some constant $$C(\varepsilon)$$ ; this bound has an application to common values of the functions $$\phi(n)$$ and $$\sigma(n)$$ (See above). We also study the distribution of Pratt trees , the tree structure formed by all of the prime chains ending at a given prime $$p$$ (and related to the Pratt certificate of primality). We prove the first nontrivial bounds on the height of the Pratt tree, valid for almost all primes $$p$$, and also develop a sophisticated stochastic model of the Pratt trees based on branching random walks. This model leads us to conjecture various behaviors of the Pratt trees, in particular that the heights have a tight probability distribution with mean close to $$e \log \log p$$.

48. Chebyshev's bias for products of two primes , Kevin Ford and Jason Sneed
Experim. Math. 19 (2010), 385-398.

49. The number of solutions of λ(x)=n , Kevin Ford and Florian Luca
INTEGERS (Proceedings of the INTEGERS conference honoring Melvyn Nathanson and Carl Pomerance) 11A (2011), Article 9.

50. Explicit constructions of RIP matrices and related problems , Jean Bourgain, Stephen J. Dilworth, Kevin Ford, Sergei Konyagin and Denka Kutzarova
Duke Math. J. 159 (2011), 145-185.
Abstract: We break a natural barrier in the explicit construction of matrices useful in compressed sensing. Let $$\Phi$$ be an $$N \times n$$ matrix. Given parameters $$k$$ and $$\delta$$, if $(1-\delta) \| \mathbf{x} \| \le \| \Phi \mathbf{x} \| \le (1+\delta) \| \mathbf{x} \|$ for any vector $$\mathbf{x}\in \mathbb{C}^N$$ with at most $$k$$ nonzero coefficients, the matrix $$\Phi$$ is said to satisfy the Restricted Isometry Property (RIP) of order $$k$$ and constant $$\delta$$. If the entries of $$\Phi$$ are chosen randomly, then with high probability, $$\Phi$$ will satisfy the RIP property if order $$k > cn/\log N.$$ All known explicit constructions do much worse, only producing the RIP property of order $$k = O(n^{1/2})$$ due to the use of coherence (requiring the columns to have pairwise small inner products). In this paper, we construct a new type of matrix that provably satisfies the RIP property with larger order. Specifically, for some specific $$\varepsilon>0$$, large $$N$$ and any $$n$$ satisfying $$N^{1-\varepsilon} \le n\le N$$, we construct RIP matrices of order $$k = n^{1/2+\varepsilon}$$ and constant $$\delta= n^{-\varepsilon}$$. Key ingredients in our proof are new estimates for sumsets in product sets and for exponential sums over sets possessing special additive structure.

In the same paper, we also give a construction of sets of $$n$$ complex numbers whose $$k$$-th moments are uniformly small for $$1\le k\le N$$ (Turán's power sum problem), which improves upon known explicit constructions when $$N$$ is very large compared to $$n$$.

51. Breaking the k2 barrier for explicit RIP matrices , Jean Bourgain, Stephen J. Dilworth, Kevin Ford, Sergei Konyagin and Denka Kutzarova
Proceedings of the 43rd Symposium on the Theory of Computing (STOC '11) (2011), 637-644.
Abstract: This is a summary of the main ideas from the previous paper No. 50. In addition, some new ideas are inserted in a key step which allows one to greatly improve the value of the constant ε appearing in the main theorem (it is still rather tiny, as it depends on a bound in additive combinatorics which is expected to be far from optimal).

52. On common values of φ(n) and σ(m), I . Kevin Ford and Paul Pollack
Acta Math. Hungarica 133 (2011), 251-271.

53. A problem of Ramanujan, Erdős and Katai on the iterated divisor function , Yvonne Buttkewicz, Christian Elsholtz, Kevin Ford and Jan-Christoff Schlage-Puchta
International Mathematical Research Notices 2012 , 4051-4061.

54. On common values of φ(n) and σ(m), II . Kevin Ford and Paul Pollack
Algebra and Number Theory 6 (2012), no. 8, 1669-1696.
Abstract: Computational evidence suggests that a positive proportion of the integers in the range of Euler's function φ(n) are also in the range of the sum-of-divisors function σ(m). In fact, up to 108, roughly half of all integers in the range of φ are also in the range of σ and vice-versa. This is misleading, however. In this paper, we prove that the intersection of the two ranges has relative density zero inside the range of φ and inside the range of σ. The proof requires the full structure theory of typical φ- and σ-values from paper No. 6 above.

55. On groups with perfect order subsets , Kevin Ford, Sergei Konyagin and Florian Luca.
Moscow J. Comb. Number Th. 2 (2012), 297-312.

56. Poisson-Dirichlet branching random walks . Louigi Addario-Berry and Kevin Ford
Ann. Appl. Prob. 23 , (1) (2013), 283-307.

57. On square values of the product of the Euler totient and sum of divisors functions . Kevin Broughan, Kevin Ford and Florian Luca
Colloq. Math. 130 (2013), 127-137.

58. On non-intersecting arithmetic progressions , Régis de la Bretèche, Kevin Ford and Joseph Vandehey
Acta Arithmetica 157 (2013), 381-392.

59. The prime number race and zeros of L-functions off the critical line. III. Kevin Ford, Sergei Konyagin and Youness Lamzouri,
Quart. J. Math. Oxford 64 (2013), 1091-1098.

60. Values of the Euler φ-function not divisible by a given odd prime, and the distribution of Euler-Kronecker constants for cyclotomic fields , Kevin Ford, Florian Luca and Pieter Moree
Math. Comp. 83 (2014), no. 287, 1447-1476.

61. Sieving very thin sets of primes, and Pratt trees with missing primes . Kevin Ford
International Mathematical Research Notices 2014 (2014), 2955-2971.

62. On Vinogradov's mean value theorem: strongly diagonal behaviour via efficient congruencing , Kevin Ford and Trevor D. Wooley
Acta Mathematica 213 (2014), 199-236.
Abstract: I. M. Vinogradov introduced in the 1930s the quantity $$J_{s,k}(N)$$, which counts the integer solutions of the system of equations $$\sum_{i=1}^s (x_i^j-y_i^j)=0 \quad (1\le j\le k)$$, where $$1\le x_i,y_i \le N$$ for all $$i$$ Estimates for the number of solutions are particularly useful in Diophantine problems such as Waring's problem, and have also led to the best known zero-free region for the Riemann zeta function (see above). The Main Conjecture for Vinogradov's system states that $J_{s,k}(N) \ll_\epsilon N^\epsilon (N^s + N^{2s-k(k+1)/2}).$ In 2011, Wooley introduced a new, powerful method known as efficient congruencing which led to a proof of this conjecture for $$s \ge k^2$$. In the "small s" range, that is $$s\le \frac12 k(k+1)$$, it is conjectured that the "diagonal" solutions (solutions with $$x_1,\ldots,x_s$$ a permutation of $$y_1,\ldots,y_s$$ ) dominate and consequently that $$J_{s,k}(X) \ll_\epsilon X^{s+\epsilon}$$. Until recently this was know only in the trivial case $$s \le k$$ and for $$s=k+1$$ . In this paper, we develop a variant of the efficient congruencing method to prove this conjecture in the much wider range $$1\le s\le \frac14 (k+1)^2$$.

63. The image of Carmichael's λ-function , Kevin Ford, Florian Luca and Carl Pomerance
Algebra and Number Theory 8 (2014), 2009-2025.
Notes: A few small typos have been corrected in the version here.

64. Unnormalized differences between zeros of L-functions , Kevin Ford and Alexandru Zaharescu
Compositio Math. 151 (2015), 230-252.

65. Large gaps between consecutive prime numbers containing perfect powers , Kevin Ford, D. R. Heath-Brown and Sergei Konyagin
in the book Analytic Number Theory, in honor of Helmut Maier's 60th birthday, C. Pomerance and M.Th. Rassias (eds.), Springer-Verlag, 2015, pp. 83-92.

66. On the parity of the number of small divisors of n , Kevin Ford, Florian Luca, Carl Pomerance and Jeffrey Shallit
in the book Analytic Number Theory, in honor of Helmut Maier's 60th birthday, C. Pomerance and M.Th. Rassias (eds.), Springer-Verlag, 2015, pp. 93-100.

67. Large gaps between consecutive prime numbers . Kevin Ford, Ben Green, Sergei Konyagin and Terence Tao
Annals of Math. 183 (2016), 935-974.
Abstract: Let $$G(x)$$ denote the largest gap between consecutive prime numbers which are less than $$x$$. A famous lower bound of Rankin from 1938 (itself an improvement upon earlier results of Westzynthius and Erdős) states that $G(x) \ge c \frac{\log x \log\log x \log\log\log\log x}{(\log\log\log x)^2}$ for some positive constant $$c$$. In the next 75 years, only the constant $$c$$ was improved, the best result being that of Pintz from 1997 that $$c=2e^{\gamma}-o(1)$$. Because the above limit was the natural limitation of a certain circle of ideas, Erdős offered a prize of \$10,000 to prove that the constant $$c$$ could be taken arbitrarily large (that is, for every $$c$$ the above bound holds if $$x$$ is sufficiently large in terms of $$c$$ ). In this paper, we solve this conjecture. The proof uses a novel probabilistic construction, together with ideas stemming from the recent breakthroughs of Green and Tao for counting solutions of linear equations over primes.
Media publicity for this paper:

68. Permutations fixing a k-set , Sean Eberhard, Kevin Ford and Ben Green
IMRN 2016 , no. 21, 6713-6731.

69. Permutations contained in transitive subgroups , Sean Eberhard, Kevin Ford and Dimitrios Koukoulopoulos
Discrete Analysis 2016: 12 , 34 pages.

70. Invariable generation of the symmetric group , Sean Eberhard, Kevin Ford and Ben Green
Duke Math. Journal 166 (2017), no. 8, 1573-1590.

71. Integers divisible by a large shifted prime . Kevin Ford.
Acta Arithmetica 178 (2017), no. 2, 163-180.

72. On the smallest simultaneous power nonresidue modulo a prime . Kevin Ford, Moubariz Z. Garaev and Sergei V. Konyagin,
Forum Mathematicum 29 (2017), no. 2, 347-355.

73. Simultaneous distributions of fractional parts of Riemann zeta zeros , Kevin Ford, Xianchang Meng and Alexandru Zaharescu
Bulletin of the London Math. Soc. 49 , no. 1, (2017), 1-9.

74. Long gaps between consecutive prime numbers , Kevin Ford, Ben Green, Sergei Konyagin, James Maynard and and Terence Tao,
J. Amer. Math. Soc., 31 (2018), no. 1, 65-105.
 Abstract: In this paper, we make a quantitative improvement to the lower bound for $$G(x)$$, the largest gap between consecutive primes less than $$x$$, see paper #67 above. We prove that for some constant $$c$$ and large $$x$$, $G(x) \ge c \frac{\log x \log\log x \log\log\log\log x}{\log\log\log x}$ improving the previous bound by a factor of $$\log\log\log x$$. There are three main ingredients in the proof. First, we utilize the probabilistic constructions from the earlier paper No. 67 above. Next, we incorporate a uniform version of the multidimensional prime detecting sieve method of Maynard which was earlier used to show that there are many primes. thirdly, we prove a generalization of a hypergraph covering theorem of Pippenger and Spencer, which allows for an essentially optimal means of translating such estimates into a result on large gaps between primes.

75. Chains of large gaps between primes , Kevin Ford, James Maynard and Terence Tao
in the book "Irregularities in the distribution of prime numbers", (J. Pintz, M. Th. Rassias, eds.), Springer, 2018, p. 1-21.

76. Dimensional lower bounds for Falconer type incidence and point configuration theorems . Jonathan DeWitt, Kevin Ford, Eli Goldstein, Steven J. Miller, Gwyneth Moreland, Eyvindur A. Palsson, and Steven Senger. 10 pages.

77. Extreme biases in prime number races with many contestants. Kevin Ford, Adam J. Harper and Youness Lamzouri. Math. Annalen, to appear.

78. Extremal properties of product sets. Kevin Ford. Trudy Matematicheskogo Instituta imeni V.A. Steklova 303 (2018), special issue dedicated to the 60th birthday of Sergei V. Konyagin. to appear.

79. Long gaps in sieved sets . Kevin Ford, Sergei Konyagin, James Maynard, Carl Pomerance and Terence Tao. 26 pages.

80. Rough integers with a divisor in a given interval. Kevin Ford. 16 pages.

### Expository/Survey/Announcement Papers

1. The distribution of totients . Kevin Ford
ERA Amer. Math. Soc. , 4 (1998), 27-34.
Abstract: This is an announcement and extended abstract of papers No. 6, 7 and 10 above.

2. Chebyshev's conjecture and the prime number race , Kevin Ford and Sergei Konyagin
Modern Problems of Number Theory and its Applications; Topical Problems Part II (Tula, Russia, 2001). (2002), 67-91.

3. Recent progress on the estimation of Weyl sums Kevin Ford
Modern Problems of Number Theory and its Applications; Topical Problems Part II (Tula, Russia, 2001). (2002), 48-66.

4. From Kolmogorov's theorem on empirical distribution to number theory . Kevin Ford
in the book "Kolmogorov's legacy in mathematics", eds. E. Charpentier et al., Editions Belin (Paris), 2004, 111-120. The printed version is in French. PDF file of English original (8 pages). See below for an updated version (appeared in the English version of the book).

5. From Kolmogorov's theorem on empirical distribution to number theory . Kevin Ford
Appeared in the book Kolmogorov's heritage in mathematics (English edition) , Editions Belin/Springer, 2007, 97-108. Updated version (with sketch of a different proof of the main result).
Abstract: This paper describes how new bounds for constrained random walks (related to Kolmogorov-Smirnov statistics) are used to study the distribution of divisors of integers in paper No. 34.

### Unpublished work

1. Simple proof of Gallagher's singular series sum estimate , unpublished 1-page note, 13-Oct-2007, arXiv:1108.3861