题解 | #等差数列#
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
import java.util.*; public class Main{ public static void main(String[] args){ Scanner sc = new Scanner(System.in); while(sc.hasNext()){ int n = sc.nextInt(); System.out.println(n*2+n*(n-1)*3/2); } } }