\bib{1966/debruijn}
\yr 1966
\mr 34:5770
\by Nicolaas G. de Bruijn
\paper On the number of positive integers $\le x$ and free of prime factors $>y$. II
\jour Indagationes Mathematicae
\issn 0019--3577
\vol 28
\pages 239--247
\endref