$$U_{900}(x, y) = \frac{2 - 2 \cos{\left(\frac{2 \arcsin{\left(\frac{3 \sqrt{3} \sqrt{x}}{2 \operatorname{abs}{\left(y - 1 \right)}} \right)}}{3} \right)}}{3 x \left(1 - y\right)}$$

$$T_{900}(n, m, k) = \frac{k {\binom{2 k + 3 n - 1}{n}} {\binom{3 k + m + 2 n - 1}{m}}}{k + n}$$