$$U_{906}(x, y) = \frac{1 - \sqrt{- 4 x y^{2} - 16 x y - 16 x + 1}}{2 x y + 4 x}$$

$$T_{906}(n, m, k) = \frac{2^{k - m + 2 n} k {\binom{k + 2 n}{m}} {\binom{k + 2 n}{n}}}{k + 2 n}$$