There is the following formulaeformula: $$ x_{n+2} = \frac{x_{n+1}^3}{2 x_{n}} + \frac{5}{2} x_n^2 x_{n+1} $$$$ x_{n+2} = \frac{x_{n+1}^3}{2 x_{n}^2} + \frac{5}{2} x_n^2 x_{n+1} $$ I'm not sure if this is a pure recurrence formulae. If you need, I may provide a proof.