规律如下：
1 = 1/1
1/2 = 2/4 = 2/(1+3)
3/13 = 3/13 = 3/(1+3+9)
1/10 = 4/40 = 4/(1+3+9+27)
5/121 = 5/121 = 5/(1+3+9+27+81)