Questa è la formula 10.4.64
$$
\text{Bi}\ (-z)\sim \pi^{-\frac{1}{2}} z^{-\frac{1}{4}} \left[\cos\left(\zeta +\frac{\pi}{4}\right) \sum\limits_{0}^\infty (-1)^kc_{2k}\zeta^{-2k} \\+\sin \left( \zeta +\frac{\pi}{4}\right) \sum\limits_{0}^\infty (-1)^kc_{2k+1} \zeta^{-2k-1}\right]\left(|\arg z|<\frac{2}{3} \pi\right)
$$