A272055 Decimal expansion of -1/(e^2 Ei(-1)), an increasing rooted tree enumeration constant associated with the Euler-Gompertz constant, where Ei is the exponential integral.

6, 1, 6, 8, 8, 7, 8, 4, 8, 2, 8, 0, 7, 2, 7, 0, 7, 1, 4, 4, 4, 9, 3, 8, 3, 4, 5, 6, 6, 2, 2, 8, 5, 4, 9, 3, 5, 2, 4, 9, 0, 0, 5, 6, 9, 3, 3, 1, 6, 8, 8, 1, 7, 8, 6, 5, 6, 6, 1, 0, 3, 3, 2, 3, 1, 9, 1, 4, 3, 7, 2, 4, 2, 5, 1, 5, 4, 7, 6, 7, 2, 7, 3, 0, 3, 3, 9, 8, 2, 5, 6, 0, 3, 1, 4, 9, 4, 8, 3, 4, 5, 1, 1

Offset: 0

Author

Jean-François Alcover, Apr 19 2016

Keywords

• nonn
• cons

Examples

			0.61688784828072707144493834566228549352490056933168817865661...
		

References

• Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 5.6 Otter's tree enumeration constants, p. 303.

Links

• G. C. Greubel, Table of n, a(n) for n = 0..10000
• F. Bergeron, Ph. Flajolet and B. Salvy, Varieties of Increasing Trees, Lecture Notes in Computer Science vol. 581, ed. J.-C. Raoult, Springer-Verlag, 1992, pp. 24-48.
• Eric Weisstein's MathWorld, Gompertz Constant
• Eric Weisstein's MathWorld, Exponential Integral
• Eric Weisstein's MathWorld, Rooted Tree
• Index entries for sequences related to mobiles

Crossrefs

Cf. A029768, A073003.

Programs

Mathematica

RealDigits[-1/(E^2*ExpIntegralEi[-1]), 10, 103][[1]]

PARI

default(realprecision, 100); 1/(exp(2)*eint1(1)) \\ G. C. Greubel, Sep 07 2018

Formula

Equals 1 / (e * A073003).

Also equals -1 / (e^2 * (gamma - Sum_{n>=1} (-1)^(n-1)/(n*n!))), where gamma is the Euler-Mascheroni constant A001620.