$$U_{806}(x, y) = \frac{1}{\left(- \frac{x \left(1 - \sqrt{1 - 4 y}\right)}{2 y} + 1\right)^{2}}$$

$$T_{806}(n, m, k) = \begin{cases}1&\text{if n=0,m=0} ,\ \\\frac{n {\binom{2 k + n - 1}{n}} {\binom{2 m + n - 1}{m}}}{m + n} \end{cases} $$