import java.util.Scanner; // 注意类名必须为 Main, 不要有任何 package xxx 信息 public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int a = sc.nextInt(); //等差数列数字个数为n //2 ,2+5 ; //3 ,2+5+8 ; 2+ (n-1)*3=6 //4, 2+5+8+11 //5,2+5+8+11+14 //7,2+5+8+11+14+17+20 //(n-1)*3=6 //...