$$U_{835}(x, y) = \frac{- y^{3} + 3 y^{2} - 3 y - \sqrt{- 4 x + y^{6} - 6 y^{5} + 15 y^{4} - 20 y^{3} + 15 y^{2} + y \left(4 x - 6\right) + 1} + 1}{2 x y^{2} - 4 x y + 2 x}$$

$$T_{835}(n, m, k) = \frac{k {\binom{k + 2 n - 1}{n}} {\binom{4 k + m + 5 n - 1}{m}}}{k + n}$$