思路：

代码：

#include<bits/stdc++.h>
using namespace std;

int main(){
    int n,a1,res;
    string str;
    while (cin >> n){
        str = "";
        a1 = n * n - n + 1;
        for (int i = 0; i < n;i++){
            str += to_string(a1 + 2 * i);
            if(i==n-1){
                break;
            }
            str += "+";
        }
        cout << str << endl;
    }

    return 0;
}