C语言编程：有一分数序列：2/1，3/2，5/3，8/5，13/8，21/13...求出这个数列

#include double Sum(int n) { int i; double sum = 0.0; double rator = 2,nator = 1,t; for(i = 0; i < n; ++i) { sum += rator / nator; t = nator; nator = rator; rator = t + nator; } return sum;} int main() { int n = 20; printf("f(%d) = %lf\