Project Euler Prob.12

Problem

The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, …

Let us list the factors of the first seven triangle numbers:

1: 1 3: 1,3 6: 1,2,3,6 10: 1,2,5,10 15: 1,3,5,15 21: 1,3,7,21 28: 1,2,4,7,14,28 We can see that 28 is the first triangle number to have over five divisors.

What is the value of the first triangle number to have over five hundred divisors?

Sol. 1

#include <stdio.h>
using namespace std;
int main()
{
	int sum = 0, i = 1;
	while(1)
	{
		int cnt = 2;
		sum += i;
		for (int j = 2; j*j < sum; j++)
		{
			if (sum % j == 0)
				cnt+=2;
		}
		if (cnt > 500)
		{
			printf("%d\n", sum);
			break;
		}
		i++;
	}
	return 0;
}