d n f d f n ( a ) = n ! 2 π i ∮ γ f ( z ) ( z − a ) n d z {\displaystyle {\frac {d^{n}f}{df^{n}}}\left(a\right)={\frac {n!}{2\pi i}}\oint _{\gamma }{\frac {f\left(z\right)}{\left(z-a\right)^{n}}}dz}
