$$U_{378}(x, y) = \frac{1 - \sqrt{\sqrt{1 - 4 y} \left(- 16 x y + 4 x\right) + 1}}{2 \sqrt{1 - 4 y}}$$

$$T_{378}(n, m, k) = \begin{cases}0&\text{if n<k} ,\ \\- \frac{\left(-1\right)^{n - 1} \cdot 4^{m} k {\binom{- k + 2 n - 1}{n - 1}} {\binom{\frac{k}{2} + m - \frac{3 n}{2} - 1}{m}}}{n} \end{cases} $$