$$U_{380}(x, y) = \frac{y}{2} + \frac{\sqrt{4 x \left(y + 1\right) + \left(y + 1\right)^{2}}}{2} + \frac{1}{2}$$

$$T_{380}(n, m, k) = \begin{cases}{\binom{k}{m}}&\text{if n=0} ,\ \\\frac{k {\binom{k - n}{m}} {\binom{k - n - 1}{n - 1}}}{n} \end{cases} $$