@article{IM2_2010_74_6_a4,
     author = {M. A. Korolev},
     title = {On the average number of power residues modulo a~composite number},
     journal = {Izvestiya. Mathematics },
     pages = {1225--1254},
     publisher = {mathdoc},
     volume = {74},
     number = {6},
     year = {2010},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2010_74_6_a4/}
}