# factorial(n) is n!;
#factorial(0,x_):=factorial(x);
#factorial(1,x_):=factorial(x)*psi(x+1);
#factorial(x_):=gamma(x+1);


factorial(-3/2):= -2sqrt(pi);
factorial(-1/2):= sqrt(pi);
factorial(1/2):= sqrt(pi)/2;
factorial(3/2):= 3/4*sqrt(pi);