$$U_{723}(x, y) = \frac{1 - \sqrt{y^{2} \left(- 4 x - 4\right) + 1}}{2 y^{2}}$$

$$T_{723}(n, m, k) = \frac{k \left(\left(-1\right)^{m} + 1\right) {\binom{k + m}{n}} {\binom{k + m - n}{\frac{m}{2}}}}{2 k + 2 m}$$