For integer $n = 1, 2, \dots$, the first few values of $\Gamma (n)$ are 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, $\dots$ (OEIS A000142). For half-integer arguments, $\Gamma (n/2)$ has the special form
$\Gamma(\frac{1}{2}n) = \frac{(n-2)!!\sqrt{\pi}}{2^{(n-1)/2}}$, (54)