$$U_{890}(x, y) = \frac{2 x + \sqrt{4 x + \left(y + 1\right)^{4}} \left(y + 1\right)^{2} + \left(y + 1\right)^{4}}{2 y + 2}$$

$$T_{890}(n, m, k) = \begin{cases}{\binom{3 k}{m}}&\text{if n=0} ,\ \\\frac{2 \left(-1\right)^{n - 1} k {\binom{3 k - 4 n}{m}} {\binom{- 2 k + 2 n - 1}{n - 1}}}{n} \end{cases} $$