$$= \frac { U _ { n } ^ { n } ( 1 + 2 ) ( n + 1 ) } { 3 n ( n + 2 ) ( n + 2 ) + 2 n - 1 - 1 - 3 n ^ { 2 } - 6 n }$$
$\frac{3\left(n+1\right)U_{n}^{n}}{3n^{3}+9n^{2}+8n-2}$
$\frac{3n\left(n+1\right)U_{n}^{n-1}}{3n^{3}+9n^{2}+8n-2}$
