题解 | #等差数列#
等差数列
http://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
数学公式:(第一个数+最后一个数)*n/2
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((2+3*n-1)*n/2); } } }