I need to find formula for $n$-th derivative of $\arcsin^k(\frac{x}{2})$.
I have found formula for
$$\left(\arcsin\frac{x}{2}\right)^{(n)}=\frac{(-i)^{n-1}(n-1)!}{\left(4-z^2\right)^{n/2}}P_{n-1}\left(\frac{i z}{\sqrt{4-z^2}}\right)$$
Where $P_n$ - Legendre polynomial.
I have found on the net formula for $n$-th derivative of composite function, however it didn't help. How can I find required formula?