$$U_{920}(x, y) = \frac{\sqrt{y \left(- 8 x - 8\right) + 1}}{4} + \frac{1}{4}$$

$$T_{920}(n, m, k) = \begin{cases}0&\text{if m = 0, n > 0} ,\ \\2^{- k}&\text{if n = 0, m = 0} ,\ \\- \frac{2^{- k + m} k {\binom{m}{n}} {\binom{- k + 2 m - 1}{m - 1}}}{m}&\text{if m > 0} \end{cases} $$