1. G. H. Hardy and J. E. Littlewood, “Contributions to the theory of the Riemann zeta-function and the theory of the distribution of primes,” Acta Math. 41 (3), 119–196 (1916).
2. I. Katai, “On oscillations of number-theoretic functions,” Acta Arith. 13, 107–122 (1967).
3. S. Gerhold, “Asymptotic estimates for some number-theoretic power series,” Acta Arith. 142, 187–196 (2010).
4. W. D. Banks, F. Luca, and I. E. Shparlinski, “Irrationality of power series for various number theoretic functions,” ManuscriptaMath. 117, 183–197 (2005).
5. S. Wigert, “Sur la série de Lambert et son application à la théorie des nombres,” ActaMath. 41 (1), 197–218 (1916).