求1!+2!+3!+4!+……+n! n=20

以下是Java和C语言两种实现方法：

Java代码实现：

import java.math.BigInteger;

public class FactorialSum {
    public static void main(String[] args) {
        int n = 20;
        BigInteger sum = BigInteger.ZERO;
        BigInteger factorial = BigInteger.ONE;
        for (int i = 1; i <= n; i++) {
            factorial = factorial.multiply(BigInteger.valueOf(i));
            sum = sum.add(factorial);
        }
        System.out.println(sum);
    }
}

C语言代码实现：

#include <stdio.h>

long long factorial(int n) {
    if (n == 0 || n == 1) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

long long fun(int n) {
    long long sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += factorial(i);
    }
    return sum;
}

int main() {
    int n = 20;
    printf("%lld", fun(n));
    return 0;
}