@article{1966-debruijn
,author={Nicolaas G. de Bruijn}
,ISSN={0019--3577}
,journal={Indagationes Mathematicae}
,MR={34:5770}
,pages={239--247}
,title={{On the number of positive integers $\le x$ and free of prime factors $>y$. II}}
,volume={28}
,year={1966}
}