Ivić, Aleksandar (). The Riemann zeta-function. The theory of the Riemann zeta-function with applications. A Wiley-Interscience Publication. New York etc.: John Wiley & Sons. pp. 33–34,407–413. ISBN978-0-471-80634-9. Zbl0556.10026.
McDaniel, Wayne L. (). „Representations of every integer as the difference of powerful numbers”. Fibonacci Quarterly. 20: 85–87.