第二篇文章...?

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int num = sc.nextInt();
            int first = (int) (Math.pow(num, 2)) - num + 1;
            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < num; i++) {
                sb.append(first + i * 2).append("+");
            }
            System.out.println(sb.substring(0, sb.length()-1).toString());
        }
    }
}

找 M 与首项的关系