Lao, Hui Xue, Exponential sums over primes formed with coefficients of primitive cusp forms, Acta mathematica Sinica. English series (Print) , 25(4), 2009, pp. 687-692
Let . f (n) be the coefficient of the logarithmic derivative for the Hecke L-function. In this paper we study the cancellation of the function . f (n) twisted with an additive character e(..n), . > 0, i.e. S f (x) = . x<n.2x . f (n)e(..n).