$$U_{873}(x, y) = \frac{2 \sqrt{3} \sin{\left(\frac{\operatorname{asin}{\left(\frac{3 \sqrt{3} \sqrt{\frac{x}{\sqrt{1 - 4 y}}}}{2} \right)}}{3} \right)}}{3 \sqrt{\frac{x}{\sqrt{1 - 4 y}}}}$$

$$TA_{984}(n, k) = \begin{cases}{4}^{n} \binom {n+j-1} {n} &\text{if k even, where j =} \frac {k} {2},\\\frac {\binom {n+j} {n} \binom {2n+2j} {n+j}} {\binom {2j} {j}}&\text{if k odd, where j =} \frac {k-1} {2},\end{cases} $$$$T_{873}(n, m, k) = \frac{k \operatorname{TA_{984}}{\left(m,n \right)} {\binom{k + 3 n - 1}{n}}}{k + 2 n}$$