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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4.  
  5. const int N = 1e6 + 1;
  6. int p[N];
  7.  
  8.  
  9. void solve() {
  10.  
  11.  
  12. 	//Calculating factors using prime sieve
  13. 	for (int i = 2; i < N; ++i) {
  14. 		if (p[i])continue;
  15. 		for (int j = i; j < N; j += i)p[j] = i;
  16. 	}
  17. 	for (int i = 2; i < N; ++i) {
  18. 		if (p[i])continue;
  19. 		for (int j = i; j < N; j += i)p[j] = i;
  20. 	}
  21.  
  22. 	auto getFactorCnt = [&](int x) {
  23. 		int ans = 1;
  24. 		while (x > 1) {
  25. 			int prime = p[x], cnt = 1;
  26. 			while (x % prime == 0)cnt++, x /= prime;
  27. 			ans *= cnt;
  28. 		}
  29. 		return ans;
  30. 	};
  31.  
  32. 	//Main code
  33. 	int res = 0;
  34. 	int n; cin >> n;
  35. 	for (int i = 1; i < n; ++i)
  36. 	{
  37. 		res  = res + getFactorCnt(n - i);
  38. 	}
  39.  
  40. 	cout << res << endl;
  41. }
  42.  
  43.  
  44.  
  45. int main() {
  46.  
  47.  
  48. #ifndef ONLINE_JUDGE
  49. 	freopen("input1.txt", "r", stdin);
  50. 	freopen("output1.txt", "w", stdout);
  51. #endif
  52.  
  53. 	// int t; cin >> t;
  54. 	int t = 1;
  55.  
  56. 	while (t--) {
  57. 		solve();
  58. 	}
  59.  
  60. 	return 0;
  61. }
Success #stdin #stdout 0.01s 7428KB
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https://ideone.com/gpZjgX
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
public

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