@article{10_4064_aa110_3_6,
     author = {Yingchun Cai and Minggao Lu},
     title = {On the upper bound for $\pi _{2}(x)$},
     journal = {Acta Arithmetica},
     pages = {275--298},
     publisher = {mathdoc},
     volume = {110},
     number = {3},
     year = {2003},
     doi = {10.4064/aa110-3-6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa110-3-6/}
}