$$U_{250}(x, y) = \frac{1}{- x^{2} - y + 1}$$

$$T_{250}(n, m, k) = \frac{\left(\left(-1\right)^{n} + 1\right) {\binom{m + \frac{n}{2}}{m}} {\binom{k + m + \frac{n}{2} - 1}{m + \frac{n}{2}}}}{2}$$