The function is defined by the integral
(1)
and is given by the Wolfram Language function ExpIntegralE[n, x]. Defining so that ,
(2)
For integer ,
(3)
Plots in the complex plane are shown above for .
The special case gives
where is the exponential integral and is an incomplete gamma function. It is also equal to
(8)
where is the Euler-Mascheroni constant.
where and are the cosine integral and sine integral.
The function satisfies the recurrence relations
In general, can be built up from the recurrence
(13)
The series expansions is given by
(14)
and the asymptotic expansion by
(15)
See alsoCosine Integral,
Et-Function,
Exponential Integral,
Gompertz Constant,
Sine Integral Related Wolfram siteshttp://functions.wolfram.com/GammaBetaErf/ExpIntegralE/ Explore with Wolfram|Alpha ReferencesAbramowitz, M. and Stegun, I. A. (Eds.). "Exponential Integral and Related Functions." Ch. 5 in Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing. New York: Dover, pp. 227-233, 1972.Press, W. H.; Flannery, B. P.; Teukolsky, S. A.; and Vetterling, W. T. "Exponential Integrals." ยง6.3 in Numerical Recipes in FORTRAN: The Art of Scientific Computing, 2nd ed. Cambridge, England: Cambridge University Press, pp. 215-219, 1992.Spanier, J. and Oldham, K. B. "The Exponential Integral Ei() and Related Functions." Ch. 37 in An Atlas of Functions. Washington, DC: Hemisphere, pp. 351-360, 1987. Referenced on Wolfram|AlphaTagBox[E, MathPlain]_n-Function Cite this as:Weisstein, Eric W. "TagBox[E, MathPlain]_n-Function." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/En-Function.html
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