Hello everybody! Here is a problem which I can't find solution, help me please if you can. So, statement is simple:

Given n ≤ 40 and non-negative integer r < 2ⁿ. Find all integers k from 0 to 2ⁿ - 1 such that

Here is a link for problem if you want to submit: https://www.e-olymp.com/en/problems/322

Thanks in advance!