$$U_{838}(x, y) = \frac{y^{3} - 3 y^{2} + 3 y + \sqrt{- 4 x + y^{6} - 6 y^{5} + 15 y^{4} - 20 y^{3} + 15 y^{2} + y \left(4 x - 6\right) + 1} - 1}{2 x y - 2 x}$$

$$T_{838}(n, m, k) = \frac{k {\binom{k + 2 n - 1}{n}} {\binom{3 k + m + 5 n - 1}{m}}}{k + n}$$