设 f1=1f_1=1f1=1, fn={fn2,2∣nfn−12+fn+12,otherwise;f_n=\begin{cases}f_{\frac{n}{2}}, 2|n \\\\ f_{\frac{n-1}{2}}+f_{\frac{n+1}{2}}, \text{otherwise;}\end{cases}fn=⎩⎨⎧f2n,2∣nf2n−1+f2n+1,otherwise;
那么, fnf_nfn 是什么级别的呢 /kel
