我能做些什么来改进我的斐波那契数生成器?

I'm solving this problem:

我解决这个问题:

G(n) is defined as

G(n) = G(n-1) + f(4n-1) , for n > 0

and G(0) = 0

f(i) is ith Fibonacci number. Given n you need to evaluate G(n)
G(n)