$$U_{73}(x, y) = \frac{\sqrt{4 x y^{2} - 8 x y + 4 x + 1} + 1}{2 y^{2} - 4 y + 2}$$

$$T_{73}(n, m, k) = \begin{cases}{\binom{2 k + m - 1}{m}}&\text{if n=0} ,\ \\\frac{k {\binom{k - n - 1}{n - 1}} {\binom{2 k + m - 2 n - 1}{m}}}{n}&\text{if n>0} \end{cases} $$