欧拉项目 Problem 12 of What is the value of the first triangle number to have over five hundred divisors

The sequence of triangle numbers is generated by adding the natural numbers. So the 7^th 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?

public class TriangleNumbers {public static void main(String args[]){Long l1=System.currentTimeMillis();for(int i=1;i<1000000;i++){if(reTriangle(numTriangle(i))>500){System.out.println(numTriangle(i));break;}}Long l2=System.currentTimeMillis();System.out.println("need time:"+(l2-l1));}public static int numTriangle(int n){int sum=0;for(int i=1;i<=n;i++){sum+=i;}return sum;}public static int reTriangle(int n){int total=0;for(int i=1;i<=n;i++){if(n%i==0){total++;}}return total;}}

76576500need time:1116423

Answer:

76576500