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 A321940 Denominators in the asymptotic expansion of the Maclaurin coefficients of exp(x/(1-x)). 2
 1, 48, 4608, 3317760, 127401984, 214035333120, 308210879692800, 2958824445050880, 5680942934497689600, 134979204123665104896000, 18141205034220590098022400, 56600559706768241105829888000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS If r(n) = A067764(n)/A067653(n) then r(n)/(exp(2*sqrt(n))/(2*n^(3/4)*sqrt(Pi*e))) has an asymptotic expansion in ascending powers of 1/sqrt(n) whose coefficients are rational numbers 1, -5/48, etc. The sequence gives the denominators of these rational numbers. Another expression for r(n), n > 0, is r(n) = M(n+1,2,1)/e, where M(a,b,z) = 1F1(a;b;z) is a confluent hypergeometric function (Kummer function). The same rational numbers, except for signs, occur in the asymptotic expansion of the Maclaurin coefficients of exp(1/(1-x))*E1(1/(1-x)), where E1(x) is an exponential integral. See Lemmas 1-2 and Theorem 5 of the preprint by Brent et al. (2018). REFERENCES L. J. Slater, Confluent Hypergeometric Functions, Cambridge University Press, 1960. LINKS Richard P. Brent, M. L. Glasser, Anthony J. Guttmann, A Conjectured Integer Sequence Arising From the Exponential Integral, arXiv:1812.00316 [math.NT], 2018. N. M. Temme, Remarks on Slater's asymptotic expansions of Kummer functions for large values of the a-parameter, Adv. Dyn. Syst. Appl., 8 (2013), 365-377. FORMULA A formula is given in Theorem 5, and a recurrence in Lemma 7, of Brent et al. (2018). EXAMPLE The asymptotic expansion is 1 - 5*h/48 - 479*h^2/4608 - 15313*h^3/3317760 + ..., where h = 1/sqrt(n). CROSSREFS The numerators are A321939. The formula in Theorem 5 of Brent et al. (2018) uses A321937(n)/A321938(n). Sequence in context: A174755 A269419 A299422 * A222846 A265666 A114721 Adjacent sequences:  A321937 A321938 A321939 * A321941 A321942 A321943 KEYWORD nonn,frac AUTHOR Richard P. Brent, Dec 08 2018 STATUS approved

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Last modified August 15 00:52 EDT 2020. Contains 336484 sequences. (Running on oeis4.)