#include <stdio.h>// __int64的范围是 [0, 2^64),即0~18446744073709551615(约1800亿亿)
static unsigned __int64 sum_fac(int n);int main(void)
{printf("test sum_fac function.\n\n");for(unsigned int k=0; k<20; k++){printf("k=%dth e sum is: %llu\n",k,sum_fac(k)); }getchar();return 0;
}/* long sum_fac(int n)
作用：求解1!+2!+3!+...+N! ，即阶乘和。
*/unsigned __int64 sum_fac(int n)
{if(0 == n)return 1L;unsigned __int64 sum = 0;//Calcunsigned __int64 tmp = 1;for(unsigned int i=1;i<=n;i++){tmp *= i;sum += tmp;}return sum;
}