$$U_{883}(x, y) = \frac{2 x + \left(y + 1\right)^{5} + \left(y + 1\right)^{2} \sqrt{4 x + y^{6} + 6 y^{5} + 15 y^{4} + 20 y^{3} + 15 y^{2} + y \left(4 x + 6\right) + 1}}{2 \left(y + 1\right)^{2}}$$

$$T_{883}(n, m, k) = \begin{cases}{\binom{3 k}{m}}&\text{if n=0} ,\ \\\frac{2 \left(-1\right)^{n - 1} k {\binom{3 k - 5 n}{m}} {\binom{- 2 k + 2 n - 1}{n - 1}}}{n} \end{cases} $$