$$U_{946}(x, y) = \frac{\left(x + y\right)^{3}}{1 - x}$$

$$T_{946}(n, m, k) = \begin{cases}{\binom{3 k}{m}} {\binom{- k + m + n - 1}{- 3 k + m + n}},\ \\0&\text{if n+m<3*k} \end{cases} $$