java - n!乘阶之和的计算 ，1!+2!+...+20!

    public static void main(String[] args) {
        // 1!+2!+...+20!
        long sum = 0;
        for (int i = 1; i <= 20; i++) {
            int cursum = 1;
            for (int j = 1; j <= i; j++) {
                cursum *= j;
            }
            sum += cursum;
        }
        System.out.println("共"+sum);

    }