Heath-Brown, D. R. and Banks, W. D. and Garaev, M. Z. and Shparlinski, I. E. (2008) Density of non-residues in Burgess-type intervals and applications. Bulletin of the London Mathematical Society, 40 . pp. 88-96.
Heath-Brown, D. R. and Banks, W. D. and Shparlinski, I. E. (2005) On the average value of divisor sums in arithmetic progressions. International Mathematics Research Notices (1). pp. 1-25.