$$U_{1280}(x, y) = \frac{2 y + \sqrt{4 y^{2} + 1}}{\left(1 - x\right)^{3}}$$

$$T_{1280}(n, m, k) = \begin{cases}1&\text{if n=0 , m=0 , k=0} ,\ \\\frac{4^{m} k {\binom{\frac{k}{2} + \frac{m}{2}}{m}} {\binom{3 k + n - 1}{n}}}{k + m},\ \\\frac{\left(-1\right)^{- \frac{k}{2} + \frac{m}{2} - \frac{1}{2}} {\binom{m}{\frac{k}{2} + \frac{m}{2} + \frac{1}{2}}} {\binom{2 m}{m}} {\binom{3 k + n - 1}{n}}}{{\binom{2 m}{k + m + 1}}},\ \\\frac{k {\binom{2 m}{m}} {\binom{k + m + 1}{2 m}} {\binom{3 k + n - 1}{n}}}{\left(k + m\right) {\binom{\frac{k}{2} + \frac{m}{2} + \frac{1}{2}}{m}}} \end{cases} $$