# §6.9 Continued Fraction

 6.9.1 $E_{1}\left(z\right)=\cfrac{e^{-z}}{z+\cfrac{1}{1+\cfrac{1}{z+\cfrac{2}{1+% \cfrac{2}{z+\cfrac{3}{1+\cfrac{3}{z+}}}}}}}\cdots,$ $|\operatorname{ph}z|<\pi$. ⓘ Symbols: $\pi$: the ratio of the circumference of a circle to its diameter, $\mathrm{e}$: base of exponential function, $E_{1}\left(\NVar{z}\right)$: exponential integral, $\operatorname{ph}$: phase and $z$: complex variable A&S Ref: 5.1.22 (special case of) Referenced by: §6.18(i) Permalink: http://dlmf.nist.gov/6.9.E1 Encodings: TeX, pMML, png See also: Annotations for 6.9 and 6