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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. int euler_f (int n) { 
  6. 	int result = n;
  7. 	for (int i = 2; i * i <= n; ++i) {
  8. 		if (n % i == 0) {
  9. 			while (n % i == 0) n /= i; 
  10. 			result -= result / i; 
  11. 		} 
  12. 	}
  13. 	if (n > 1) result -= result / n; 
  14. 	return result;
  15. }
  16.  
  17. int main() {
  18. 	int n;
  19. 	cin >> n;
  20. 	int sum = 0;
  21. 	for (int i = 2; i <= n; ++i) {
  22. 		sum += euler_f(i);
  23. 	}
  24. 	cout << sum;
  25. 	return 0;
  26. }
Success #stdin #stdout 0s 4520KB
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https://ideone.com/kTx8qr
euler function
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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