a = − n − 2 π z n − 2 z π 2 + 1 2 b + 1 4 + z 2 ( 1 3 − 4 π − 2 ) + z − ( b − 1 ) 2 + 1 4 4 π z n + 𝒪 ( 1 n ) a=-n-\frac{2}{\pi}\sqrt{zn}-\frac{2z}{\pi^{2}}+\tfrac{1}{2}b+\tfrac{1}{4}+\frac{z^{2}\left(\frac{1}{3}-4\pi^{-2}\right)+z-(b-1)^{2}+\frac{1}{4}}{4\pi\sqrt{zn}}+\mathcal{O}\left(\frac{1}{n}\right)