$$U_{276}(x, y) = x^{3} + x + y$$

$$T_{276}(n, m, k) = \frac{\left(\left(-1\right)^{- k + m + n} + 1\right) {\binom{k}{m}} {\binom{k - m}{- \frac{k}{2} + \frac{m}{2} + \frac{n}{2}}}}{2}$$