$$U_{225}(x, y) = \frac{- 2 x - \sqrt{1 - 4 x} + \sqrt{2} \sqrt{8 x^{4} y + 2 x^{2} - 4 x + \sqrt{1 - 4 x} \left(2 x - 1\right) + 1} + 1}{4 x^{2}}$$

$$T_{225}(n, m, k) = \begin{cases}1&\text{if n=0 and m=0} ,\ \\\frac{k {\binom{k - m - 1}{m - 1}}}{m}&\text{if n=0 and m>0} ,\ \\\frac{2 k {\binom{k - m - 1}{m}} {\binom{2 k - 4 m + 2 n - 1}{n - 1}}}{n} \end{cases} $$