@article{MZ_1968__105_170961,
     author = {Leon Bernstein},
     title = {Multiplicative {Twins} and {Primitive} {Roots.}},
     journal = {Mathematische Zeitschrift},
     pages = {49--58},
     publisher = {mathdoc},
     volume = {105},
     year = {1968},
     zbl = {0165.05704},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__105_170961/}
}