Some normal numbers generated by arithmetic functions

Abstract

Let $g\ge 2$. A real number is said to be g-normal if its base g expansion contains every finite sequence of digits with the expected limiting frequency. Let ϕdenote Euler's totient function, let σbe the sum-of-divisors function, and let λbe Carmichael's lambda-function. We show that if f is any function formed by composing ϕ, σ, or λ, then the number \[ 0. f(1) f(2) f(3) \dots \] obtained by concatenating the base g digits of successive f-values is g-normal. We also prove the same result if the inputs 1, 2, 3, \dots are replaced with the primes 2, 3, 5, \dots. The proof is an adaptation of a method introduced by Copeland and Erdos in 1946 to prove the 10-normality of 0.235711131719\ldots.