$$U_{255}(x, y) = \frac{1}{\sqrt{- 4 x^{2} - 4 y + 1}}$$

$$T_{255}(n, m, k) = \begin{cases}\frac{\left(\left(-1\right)^{n} + 1\right) {\binom{m + \frac{n}{2}}{m}} {\binom{\frac{k}{2} + m + \frac{n}{2}}{m + \frac{n}{2}}} {\binom{k + 2 m + n}{\frac{k}{2} + m + \frac{n}{2}}}}{2 {\binom{k}{\frac{k}{2}}}}&\text{if k even} ,\ \\\frac{\left(\left(-1\right)^{n} + 1\right) {\binom{m + \frac{n}{2}}{m}} {\binom{\frac{k}{2} + m + \frac{n}{2} - \frac{1}{2}}{m + \frac{n}{2}}} {\binom{k + 2 m + n - 1}{\frac{k}{2} + m + \frac{n}{2} - \frac{1}{2}}}}{2 {\binom{k - 1}{\frac{k}{2} - \frac{1}{2}}}}&\text{if k odd} \end{cases} $$