“…The approaches are either using Rankin-Selberg estimates, or Chebotarev density theorem, or distribution of B-free numbers, or the bounds on certain exponential sums, etc., (cf. [BO01], [Alk03], [Alk05], [AZ05a], [AZ08], [DG14]). For example, the approach to the non-vanishing problem through the distribution of B-free numbers has been considered by Alkan and Zaharescu ([AZ05b]), Matomäki ([Mat12]), and Kowalski, Robert, and Wu ( [KRW07]), and many more.…”