$$U_{252}(x, y) = \frac{- x^{2} - \sqrt{x^{4} - 2 x^{2} - 4 y + 1} + 1}{2 y}$$

$$T_{252}(n, m, k) = \frac{k \left(\left(-1\right)^{n} + 1\right) {\binom{m + \frac{n}{2}}{m}} {\binom{k + 2 m + \frac{n}{2} - 1}{m + \frac{n}{2}}}}{2 k + 2 m}$$