C++for循环问题，输入n，循环n次，求1+1/2+2/3+3/5…的值

输入n，循环n次，求1+1/2+2/3+3/5…的值，用for循环

没看出来分母的规律。。。

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    int n = 0, i = 0;
    scanf("%d", &n);
    double* a = (double*)malloc(sizeof(double) * (n + 1));
    double sum = 0;
    for (i = 0; i <= n; i++)
    {
        a[i] = (i == 0 || i == 1) ? 1 : a[i - 2] + a[i - 1];
    }
    for (i = 0; i < n; i++)
    {
        sum += a[i ] / a[i + 1];
    }
    printf("%lf\n", sum);
    return 0;
}