$$U_{108}(x, y) = \frac{- x - \sqrt{x^{2} - 2 x + y \left(4 x - 4\right) + 1} + 1}{2 y}$$

$$T_{108}(n, m, k) = \begin{cases}1&\text{if m=0 and n=0} ,\ \\\frac{k {\binom{m + n}{m}} {\binom{k + 2 m - 1}{k + m}}}{m + n} \end{cases} $$