@article{04173055, title = {Tau numbers, natural density, and Hardy and Wright's theorem 437.}, journal = {International Journal of Mathematics and Mathematical Sciences}, volume = {13}, year = {1990}, pages = {383-386}, doi = {10.1155/S0161171290000576}, zbl = {0713.11002}, language = {en}, url = {http://dml.mathdoc.fr/item/04173055} }
Kennedy, Robert E.; Cooper, Curtis N. Tau numbers, natural density, and Hardy and Wright's theorem 437.. International Journal of Mathematics and Mathematical Sciences, Tome 13 (1990) pp. 383-386. doi : 10.1155/S0161171290000576. http://gdmltest.u-ga.fr/item/04173055/