I am looking for a solution/resource that has the complete solution for the following problem. I think it's known as the C/Kosterman summation (i'm not sure how the name is spelled, nor could I find it on the internet). We study it in a Intro to Analytic Number Theory course. It's supposed to be a known problem, but we can't find any information on it.
Here's a backup link in case you can't open the first one. Thank you.