Mean Values and Normal Order of a Successive-Iterate Ratio of Dedekind's Arithmetic Function

Source abstract

We obtain asymptotic formulas for the three sums $$\sum_{n\le x}\frac{ψ(ψ(n))}{ψ(n)},\qquad \sum_{n\le x}\frac{ψ(n)}{ψ(ψ(n))},\qquad \sum_{n\le x}\log\frac{ψ(ψ(n))}{ψ(n)},$$ where $ψ$ denotes Dedekind's arithmetic function. We also determine the normal order of the successive-iterate ratio; more precisely, $$\frac{ψ(ψ(n))}{ψ(n)} \sim \frac{6e^γ}{π^2}\log_3 n$$ for almost all positive integers $n$.