题解 | #等差数列#
等差数列
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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) {
final int D = 3;
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
int sum = (4 + (num - 1)*D)*num/2;
System.out.println(sum);
}
}
套公式
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