Schoenfeld, Lowell (1976). "Sharper Bounds for the Chebyshev Functions ϑ(x) and ψ(x). II". Mathematics of Computation. 30 (134): 337–360. doi:10.2307/2005976. JSTOR2005976. MR0457374.
Jørgensen, Bent; Martínez, José Raúl; Tsao, Min (1994). "Asymptotic behaviour of the variance function". Scandinavian Journal of Statistics. 21 (3): 223–243. JSTOR4616314. MR1292637.
Schoenfeld, Lowell (1976). "Sharper Bounds for the Chebyshev Functions ϑ(x) and ψ(x). II". Mathematics of Computation. 30 (134): 337–360. doi:10.2307/2005976. JSTOR2005976. MR0457374.
Jørgensen, Bent; Martínez, José Raúl; Tsao, Min (1994). "Asymptotic behaviour of the variance function". Scandinavian Journal of Statistics. 21 (3): 223–243. JSTOR4616314. MR1292637.
Guy, Richard K. (2004). Unsolved Problems in Number Theory (3rd ed.). Springer-Verlag. §A4, p. 13–15. ISBN978-0-387-20860-2. Zbl1058.11001. This book uses the notation π(x;a,c) where this article uses πc,a(x) for the number of primes congruent to a modulo c.