\[n!U\left(n+\tfrac{1}{2},z\right)=i^{n}e^{-\frac{1}{2}z^{2}}\operatorname{erfc}%
(z/\sqrt{2})U\left(-n-\tfrac{1}{2},iz\right)+\sum_{m=1}^{\left\lfloor\frac{1}{%
2}n+\frac{1}{2}\right\rfloor}U\left(2m-n-\tfrac{1}{2},z\right),\]