计算算式1+21+22+23+…+2n 的值。
注意：n由键盘输入，且2 ≤ n ≤10。
package sixth;import java.util.Scanner;public class two { public static void main(String[] args) { Scanner s = new Scanner(System.in); System.out.print("输入:"); int n = s.nextInt(); int num = 0; for (int i = 0; i < n; i++) { num = num + (21+i); } System.out.print(num+1); }}