$$U_{138}(x, y) = \frac{2 x + \sqrt{- 4 x - 4 y + 1} - 1}{- 2 x^{2} - 2 y}$$

$$T_{138}(n, m, k) = \begin{cases}{\binom{k + m - 1}{m}}&\text{if n=0} ,\ \\\frac{k {\binom{k + 2 m + n}{m}} {\binom{2 k + 2 m + 2 n}{n}}}{k + 2 m + n} \end{cases} $$