It's been many years since I studied maths, and I'm trying to figure out the half factorials $(7/2)!$ without a calculator.
I did $(7/2) \times (5/2) \times (3/2) \times (1/2) = (105/16) ^ \pi = 1.82$ (as per a little tutorial I'm doing).
However, if I put $(7/2)!$ in the calculate I get $11.631$
Am I completely off target here? Sorry if this is elementary - I'm basically starting from the beginning again.
** UPDATE **
Despite the real issue being not knowing how to use the damn calculator properly - I now have a better understanding of this subject thanks to all your comments.
You can work out the half-factorials from the volumes of the spheres, which take the form of
$$ v(n) = \pi^{n/2}d^n/(n/2)! $$
For $n=3$ this gives $4\pi / 3$, makes $(3/2)! = 3 \sqrt{\pi}/4$.
One then finds that $\frac 72! = \frac 72 \frac 52 \frac 32 \frac 12 \sqrt\pi$