## COMMON VALUES OF THE ARITHMETIC FUNCTIONS φ AND σ

Citations: | 4 - 3 self |

### BibTeX

@MISC{Ford_commonvalues,

author = {Kevin Ford and Florian Luca and Carl Pomerance},

title = {COMMON VALUES OF THE ARITHMETIC FUNCTIONS φ AND σ},

year = {}

}

### OpenURL

### Abstract

ABSTRACT. We show that the equation φ(a) = σ(b) has infinitely many solutions, where φ is Euler’s totient function and σ is the sum-of-divisors function. This proves a 50-year old conjecture of Erdős. Moreover, we show that there are infinitely many integers n such that φ(a) = n and σ(b) = n each have more than n c solutions, for some c> 0. The proofs rely on the recent work of the first two authors and Konyagin on the distribution of primes p for which a given prime divides some iterate of φ at p, and on a result of Heath-Brown connecting the possible existence of Siegel zeros with the distribution of twin primes. 1.