$$U_{799}(x, y) = \frac{2 x y + 2 x - \sqrt{4 x y + 4 x + 1} + 1}{2 x^{2}}$$

$$T_{799}(n, m, k) = \frac{2 \left(-1\right)^{n} k {\binom{2 k + n}{m}} {\binom{2 k + 2 n - 1}{2 k + n - 1}}}{2 k + n}$$