@article{10_4064_aa_49_3_263_275,
     author = {Helmut Maier and Carl Pomerance},
     title = {On the number of distinct values of {Euler's} \ensuremath{\varphi}-function},
     journal = {Acta Arithmetica},
     pages = {263--275},
     publisher = {mathdoc},
     volume = {49},
     number = {3},
     year = {1987},
     doi = {10.4064/aa-49-3-263-275},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-49-3-263-275/}
}