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 A067653 Denominators of the coefficients in exp(x/(1-x)) power series. 7
 1, 1, 2, 6, 24, 40, 720, 5040, 4480, 362880, 3628800, 13305600, 479001600, 6227020800, 29059430400, 1307674368000, 1609445376000, 13173608448000, 6402373705728000, 121645100408832000, 810967336058880000, 4644631106519040000, 86461594444431360000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Define c(n)=A067764(n)/A067653(n). For a given sequence s(n) consider P[s(n)](z):=e^(-z/(1-z))*Sum_{k>=0} s(k)c(k)z^k. Regarding complex valued abelian limitation the following holds true: if s(n) is convergent (to the limit s) then lim P[s(n)](z)=s as z tends to +1 in a certain sub-domain D of the unit circle. There are two constraints: (1) D contains the line [0,1[. (2) There is a d>0 such that the intersection of {w|Re(w)>1-d} and D is a nonempty subset of a generalized Stolz set defined by {w||Im(w)|<=t*(1-Re(w))^(3/2)}, t<1. If z tends to +1 from outside such a domain that limit doesn't exist in general. - Hieronymus Fischer, Oct 20 2010 There is a significant overlap between the terms of this sequence and the terms of factorials (A000142): 44 of the first 100 terms of this sequence are also factorials. - Harvey P. Dale, Oct 27 2011 If there is no cancellation in the defining sum, a(n) = n!. In particular, a(p) = p! for prime p. In any case a(n) | n!. - Charles R Greathouse IV, Oct 27 2011 REFERENCES K. Knopp "Theory and application of infinite series" Dover p. 547 O. Perron "Uber das infinitare Verhalten der koeffizienten einer gewissen Potenzreihe", Archiv d. math.u.Phys.(3), Vol. 22, pp. 329-340. 1914 H. Fischer, Eine Theorie komplexwertiger Abelscher Limitierungsmethoden (A theory of complex valued abelian limitation methods), Dissertation (1987), pp. 29-32. K. Zeller, W. Beekmann, Theorie der Limitierungsverfahren, Springer-Verlag, Berlin (1970). LINKS Alois P. Heinz, Table of n, a(n) for n = 0..450 Richard P. Brent, M. L. Glasser, Anthony J. Guttmann, A Conjectured Integer Sequence Arising From the Exponential Integral, arXiv:1812.00316 [math.NT], 2018. D. Borwein, On methods of summability based on power series, Proc. Royal Soc. Edinburgh, Sect. A  Volume 64 / Issue 04 / January 1957, pp 342-349. FORMULA a(n) is the denominator of Sum_{i=1..n} binomial(n-1, i-1)/i!. EXAMPLE exp(x/(1-x)) = 1 + x + (3/2)*x^2 + (13/6)*x^3 + (73/24)*x^4 + (167/40)*x^5 + (4051/720)*x^6 + (37633/5040)*x^7 + (43817/4480)*x^8 + (4596553/362880)*x^9 + ... . MAPLE b:= proc(n) option remember; `if`(n=0, 1,       add((n-k)*b(k), k=0..n-1)/n)     end: a:= n-> denom(b(n)): seq(a(n), n=0..25);  # Alois P. Heinz, May 12 2016 MATHEMATICA Denominator[Rest[CoefficientList[Series[Exp[x/(1-x)], {x, 0, 20}], x]]] (* Harvey P. Dale, Oct 26 2011 *) PROG (PARI) apply(x->denominator(x), Vec(exp(x/(1-x)))) \\ Charles R Greathouse IV, Oct 27 2011 (MAGMA) m:=30; R:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!(Exp(x/(1-x)))); [Denominators(b[n]): n in [1..m]]; // G. C. Greubel, Dec 04 2018 (Sage) [denominator(sum(binomial(n-1, j-1)/factorial(j) for j in (1..n))) for n in range(30)] # G. C. Greubel, Dec 04 2018 CROSSREFS Cf. A067764. Sequence in context: A257546 A274038 A143383 * A090755 A192196 A000496 Adjacent sequences:  A067650 A067651 A067652 * A067654 A067655 A067656 KEYWORD nonn,frac AUTHOR Benoit Cloitre, Feb 03 2002 EXTENSIONS a(0)=1 prepended by Alois P. Heinz, May 12 2016 STATUS approved

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Last modified January 20 04:43 EST 2019. Contains 319323 sequences. (Running on oeis4.)