$$U_{826}(x, y) = \frac{1}{- x y + 1}$$

$$\delta{(a, b)} = \begin{cases}1&\text{if a = b},\\ 0 \end{cases} $$$$T_{826}(n, m, k) = \delta{\left(m,n \right)} {\binom{k + n - 1}{n}}$$