A problem concerning a character sum. Teske, Edlyn, Williams, Hugh C. (1999) Experimental Mathematics
Arithmetical sums in regular convolutions. V. Sita Ramaiah (1978) Journal für die reine und angewandte Mathematik
Averages of Euler products, distribution of singular series and the ubiquity of Poisson distribution Emmanuel Kowalski (2011) Acta Arithmetica