2/3,3/2.4/3,8/3
4/6,9/6,8/6.16/6
奇数项分子是 2^2,2^3.
偶数项分子式3^2,4^2.
下一项是16/6=8/3
2/3,3/2.4/3,8/3,8/3,25/6