$$U_{893}(x, y) = \frac{1}{\left(1 - y\right)^{2} \left(- x \left(1 - y\right) + 1\right)^{2}}$$

$$T_{893}(n, m, k) = {\binom{2 k + n - 1}{n}} {\binom{2 k + m - n - 1}{m}}$$