Closed formula for physicist's Hermite polynomials

Theorem

The following formula holds: $$H_n(x)=\displaystyle\sum_{k=0}^{\left\lfloor \frac{n}{2} \right\rfloor} \dfrac{(-1)^k n! (2x)^{n-2k}}{k! (n-2k)!},$$ where $H_n$ denotes the physicist's Hermite polynomials, $\left\lfloor \frac{n}{2} \right\rfloor$ denotes the floor function, and $k!$ denotes the factorial.

References

• 1960: Earl David Rainville: Special Functions ... (previous) ... (next): $103. (2)$