My question concerns a technical step in the proof of Linnik's theorem on the least prime in an arithmetic progression, as presented in Chapter 18 of Iwaniec-Kowalski: Analytic number theory. The ...
Carlitz showed necessary and sufficient conditions for an arithmetic function to be a linear combination of two multiplicative functions. He mentions the possibility of generalizing to $k$ ...
Is there an explicit formula for the number of fourth powers mod n? Finch & Sebah  give theorems, partially folklore, for squares and cubes mod n, but I don't know of a similar formula for ...