思想如下，有一对兔子，从出生后第三个月开始繁殖。小兔子长到第三个月后又生一对兔子，假设兔子不死，问第20个月有多少个兔子，我输出的兔子总是是196608..求解
#include <stdio.h>
int main()
{
    int i = 1 , j = 1 , k , sum = 0;
    for(k = 1 ;k <= 20 ; k ++)
    {
        if (k == 1)
        {
            sum = i ;
        }
        if (k == 2)
        {
            sum = j ;
        }
        if (k > 2 && k <= 20)
        {
            sum = i + j;
            i = j;
            j = i + j;
        }
    }
    for (k = 1 ; k <= 20 ; k ++)
    {
        printf("%8d",sum) ;
        if (k % 5 == 0)
        printf("\n");
    }
    return 0 ;
}