$$U_{1259}(x, y) = \left(1 - y\right)^{3} \left(- \frac{x}{\left(1 - y\right)^{3}} + 1\right)^{3}$$

$$T_{1259}(n, m, k) = {\binom{3 k + n - 1}{n}} {\binom{3 k + m + 3 n - 1}{m}}$$