Codeforces.1359E Modular Stability

1.Problem
https://codeforces.com/contest/1359/problem/E

2.Idea
a1 must be a divisor of a2..aN.

3.Source

 Int fact[N], invfact[N], inv[N];  
 void init()  
 {  
      fact[0] = 1;  
      for (int i = 1; i < N; i++) {  
           fact[i] = fact[i - 1] * i % MOD;  
      }  
      inv[1] = 1;  
      for (int i = 2; i < N; i++) {  
           inv[i] = -inv[MOD%i] * (MOD / i) % MOD;  
           if (inv[i] < 0) inv[i] += MOD;  
      }  
      invfact[0] = 1;  
      for (int i = 1; i < N; i++) {  
           invfact[i] = invfact[i - 1] * inv[i] % MOD;  
      }  
 }  
 Int nCk(Int n, Int k)  
 {  
      return fact[n] * invfact[k] % MOD * invfact[n - k] % MOD;  
 }  
 Int nPk(Int n, Int k)  
 {  
      return fact[n] * invfact[n - k] % MOD;  
 }  
 Int n, k;  
 int main()  
 {  
      cin >> n >> k;  
      init();  
      Int ans = 0;  
      for (int i = 1; i <= n; i++) {  
           int num = (n / i);  
           if (num >= k) {  
                ans = (ans + nCk(num - 1, k - 1)) % MOD;  
           }  
      }  
      cout << ans << endl;  
      return 0;  
 }