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  1. #include<stdio.h>
  2. #include<math.h>
  3.  
  4. int is_triangular(unsigned long int n)
  5. {
  6. 	// k**2 + k - 2n = 0
  7. 	// D = sqrt(1 + 8n)
  8. 	// k = (-1 + D) / 2
  9.  
  10. 	double D = sqrt(1 + 8 * n);
  11. 	if(D - floor(D) == 0)
  12. 		if( ((unsigned long)D) % 2 == 1)
  13. 			return 1;
  14. 	return 0;
  15. }
  16.  
  17. int main()
  18. {
  19. 	unsigned long int n;
  20. 	scanf("%lu", &n);
  21.  
  22. 	if(n == 1)
  23. 	{
  24. 		printf("NO");
  25. 		return 0;
  26. 	}
  27.  
  28. 	unsigned long int i;
  29. 	for(i=1; (i * (i+1) / 2) <= (n/2) ; ++i)
  30. 	{
  31. 		unsigned long int triangular = i * (i+1) / 2;
  32. 		if(is_triangular(n-triangular))
  33. 		{
  34. 			printf("YES");
  35. 			return 0;
  36. 		}
  37. 	}
  38. 	printf("NO");
  39. 	return 0;
  40. }
Success #stdin #stdout 0s 4316KB
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816761542
stdout
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YES
https://ideone.com/RCJkDp
language:
C (gcc 8.3)
created:
5 years ago
visibility:
public

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