$$U_{528}(x, y) = - \frac{\sqrt{4 x \left(1 - y\right)^{2} + \frac{1}{\left(1 - y\right)^{2}}}}{2} + \frac{1}{2 - 2 y}$$

$$T_{528}(n, m, k) = \begin{cases}0&\text{if n<k } ,\ \\- \frac{k {\binom{k - n - 1}{n - 1}} {\binom{k + m - 4 n - 1}{m}}}{n} \end{cases} $$