@article{IM2_1970_4_2_a2,
     author = {A. A. Karatsuba},
     title = {Sums of characters over prime numbers},
     journal = {Izvestiya. Mathematics},
     pages = {303--326},
     year = {1970},
     volume = {4},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1970_4_2_a2/}
}