http://139.196.53.116/ml/index.php/action/login?_=d5148d073bbd818c3900ea67310e73ca
https://www.zhihu.com/question/429554840/answer/15670907541.$$F_{a+b-1}=F_aF_b+F_{a-1}F_{b-1}$$
2.$$gcd(F_a,F_b)=F_{gcd(a,b)}$$