$$U_{660}(x, y) = \frac{\sqrt{4 x + 1} + 1}{2 \sqrt{1 - 4 y}}$$

$$T_{660}(n, m, k) = \begin{cases}4^{m} {\binom{\frac{k}{2} + m - 1}{m}}&\text{if n=0} ,\ \\\frac{\left(-1\right)^{n - 1} \cdot 4^{m} k {\binom{- k + 2 n - 1}{n - 1}} {\binom{\frac{k}{2} + m - 1}{m}}}{n}&\text{if n>0} \end{cases} $$