\[\mathbf{K}_{\nu}\left(\lambda\nu\right)\sim\frac{(\tfrac{1}{2}\lambda\nu)^{\nu%
-1}}{\sqrt{\pi}\Gamma\left(\nu+\tfrac{1}{2}\right)}\sum_{k=0}^{\infty}\frac{k!%
c_{k}(\lambda)}{\nu^{k}},\]