$$U_{1260}(x, y) = \frac{1 - \sqrt{1 - 4 y}}{2 y \left(- \frac{x \left(1 - \sqrt{1 - 4 y}\right)}{2 y} + 1\right)^{3}}$$

$$T_{1260}(n, m, k) = \frac{\left(k + n\right) {\binom{3 k + n - 1}{n}} {\binom{k + 2 m + n - 1}{m}}}{k + m + n}$$