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 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. 1
 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 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 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 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. EXAMPLE 0.61688784828072707144493834566228549352490056933168817865661... MATHEMATICA RealDigits[-1/(E^2*ExpIntegralEi[-1]), 10, 103][[1]] PROG (PARI) default(realprecision, 100); 1/(exp(2)*eint1(1)) \\ G. C. Greubel, Sep 07 2018 CROSSREFS Cf. A029768, A073003. Sequence in context: A301817 A011300 A222068 * A157292 A159828 A131114 Adjacent sequences:  A272052 A272053 A272054 * A272056 A272057 A272058 KEYWORD nonn,cons AUTHOR Jean-François Alcover, Apr 19 2016 STATUS approved

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Last modified April 17 05:36 EDT 2021. Contains 343059 sequences. (Running on oeis4.)