“…There exists a vast literature on this particular subject: We only refer to the works of Huxley [7], [8], Hafner [4], and Soundararajan [17] for the planar case, for the papers by Chamizo & Iwaniec [1], HeathBrown [5], and Tsang [18] for dimension n = 3 , and to the monographs of Walfisz [20], and Krätzel [14], [15], as well as to the recent, quite comprehensive, survey article [9].…”