$$U_{25}(x, y) = \frac{- x y - x - \sqrt{x^{2} y^{2} + x^{2} - 2 x + y \left(- 2 x^{2} - 2 x\right) + 1} + 1}{2 x^{2} y}$$

$$T_{25}(n, m, k) = \frac{k {\binom{k + n}{m}} {\binom{k + n}{- m + n}}}{k + n}$$