public class Solution { public int Sum_Solution(int n) { return (n + fun(n,n)) >> 1; //把这道题带入等差数列的公式即可 }

public int fun(int n1,int n2) {//用加法求n^2
	if(n2 == 1) return n1;
	
	return n1 + fun(n1,--n2);
}

}