$$U_{191}(x, y) = \frac{y - \sqrt{2 x y \sqrt{1 - 4 y} - 2 x y + y^{2}}}{2 x y}$$

$$T_{191}(n, m, k) = \frac{k {\binom{k + 2 n - 1}{n}} {\binom{k + 2 m + n - 1}{m}}}{k + m + n}$$