$$U_{1366}(x, y) = \frac{2 \sqrt{3} \sin{\left(\frac{\operatorname{asin}{\left(\frac{3 \sqrt[4]{3} \sqrt{\frac{x \sin{\left(\frac{\operatorname{asin}{\left(3 \sqrt{3} \sqrt{y} \right)}}{3} \right)}}{\sqrt{y}}}}{2} \right)}}{3} \right)}}{3 \sqrt{x}}$$

$$T_{1366}(n, m, k) = \begin{cases}1&\text{if n=0 , m=0 , k=0} ,\ \\\frac{4^{m} k {\binom{k + 3 n - 1}{n}} {\binom{\frac{k}{2} + 3 m + n - 1}{m}}}{k + 4 m + 2 n}&\text{if k even} ,\ \\\frac{k {\binom{k + 3 n - 1}{n}} {\binom{\frac{k}{2} + 3 m + n - \frac{1}{2}}{m}} {\binom{k + 6 m + 2 n - 1}{\frac{k}{2} + 3 m + n - \frac{1}{2}}}}{\left(k + 4 m + 2 n\right) {\binom{k + 4 m + 2 n - 1}{\frac{k}{2} + 2 m + n - \frac{1}{2}}}}&\text{if k odd} \end{cases} $$