编写函数求n!，主函数通过调用函数实现sum=1!+2!+…n!(n由键盘输入)

以下是Python实现：

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)

n = int(input("请输入n的值："))
sum = 0
for i in range(1, n+1):
    sum += factorial(i)

print("1! + 2! + ... + n! =", sum)

以下是Java实现：

import java.util.Scanner;

public class Main {
    public static int factorial(int n) {
        if (n == 0) {
            return 1;
        } else {
            return n * factorial(n-1);
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入n的值：");
        int n = scanner.nextInt();
        int sum = 0;
        for (int i = 1; i <= n; i++) {
            sum += factorial(i);
        }
        System.out.println("1! + 2! + ... + n! = " + sum);
    }
}