$$U_{156}(x, y) = \frac{\sqrt{4 x y^{3} + 12 x y^{2} + 12 x y + 4 x + 1}}{2} + \frac{1}{2}$$

$$T_{156}(n, m, k) = \begin{cases}1&\text{if m=0, n=0} ,\ \\0&\text{if n=0} ,\ \\\frac{\left(-1\right)^{n - 1} k {\binom{3 n}{m}} {\binom{- k + 2 n - 1}{n - 1}}}{n}&\text{if n>0} \end{cases} $$