description: Theofanis really likes sequences of positive integers, thus his teacher (Yeltsa Kcir) gave him a problem about a sequence that consists of only special numbers.
  
  Let's call a positive number special if it can be written as a sum of different non-negative powers of n. For example, for n = 4 number 17 is special, because it can be written as 4^0 + 4^2 = 1 + 16 = 17, but 9 is not.
  
  Theofanis asks you to help him find the k-th special number if they are sorted in increasing order. Since this number may be too large, output it modulo 10^9+7.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 10^4) — the number of test cases.
  
  The first and only line of each test case contains two integers n and k (2 ≤ n ≤ 10^9; 1 ≤ k ≤ 10^9).
  
  Output
  
  For each test case, print one integer — the k-th special number in increasing order modulo 10^9+7.
  
  Example
  
  Input
  
  
  3
  3 4
  2 12
  105 564
  
  
  Output
  
  
  9
  12
  3595374
  
  Note
  
  For n = 3 the sequence is [1,3,4,9...]
solution: #include <bits/stdc++.h>
  using namespace std;
  int main() {
    const long long MOD = 1000000007;
    int t;
    cin >> t;
    for (int _t = 0; _t < t; _t++) {
      int n;
      cin >> n;
      int k;
      cin >> k;
      int binary_k[32];
      int powers_of_two[32];
      powers_of_two[0] = 1;
      for (int i = 1; i < 32; i++) {
        powers_of_two[i] = powers_of_two[i - 1] * 2;
      }
      for (int i = 31; i >= 0; i--) {
        binary_k[i] = k / powers_of_two[i];
        k %= powers_of_two[i];
      }
      long long counter = 0;
      long long kth_power_of_n = 1;
      for (int i = 0; i < 32; i++) {
        counter += binary_k[i] * kth_power_of_n;
        counter %= MOD;
        kth_power_of_n *= n;
        kth_power_of_n %= MOD;
      }
      cout << counter << endl;
    }
  }
  