A239897 -id:A239897 - cp's OEIS frontend

A055505 Numerators in expansion of (1-x)^(-1/x)/e.

1, 1, 11, 7, 2447, 959, 238043, 67223, 559440199, 123377159, 29128857391, 5267725147, 9447595434410813, 1447646915836493, 225037938358318573, 29911565062525361, 3651003047854884043877, 38950782815463986767

Offset: 0

N. J. A. Sloane, Jul 11 2000

From Miklos Kristof, Nov 04 2007: (Start) This is also the sequence of numerators associated with expansion of (1+x)^(1/x).
(1 + x)^(1/x) = exp(1)*(1 - 1/2*x + 11/24*x^2 - 7/16*x^3 + 2447/5760*x^4 - 959/2304*x^5 + 238043/580608*x^6 - ...).
(1+x)^(1/x) = exp(log(1+x)/x) = exp(1)*exp(-x/2)*exp(x^2/3)*exp(x^3/4)*...
Let a(n) be this sequence, let b(n) be A055535. Then (1+x)^(1/x)=exp(1)*a(n)/b(n) x^n.
a(n)/b(n) = Sum_{i>=n} s(i,i-n)/i! where s(n,m) is a Stirling number of the first kind.
exp(1) = 1 + Sum_{i>=1} s(i,i)/i!, for the n=1 case.
a(1)/b(1) = 1/1 because 1+1/1!+1/2!+1/3!+1/4!+... = exp(1)
a(2)/b(2) = 1/2 because 1/2!+3/3!+6/4!+10/5!+... = 1/2*exp(1)
a(3)/b(3) = 11/24 because 2/3!+11/4!+35/5!+85/6!+... = 11/24*exp(1)
a(4)/b(4) = 7/16 because 6/4!+50/5!+225/6!+735/7!+... = 7/16*exp(1) (End)

			1+1/2*x+11/24*x^2+7/16*x^3+2447/5760*x^4+...
1, -1/2, 11/24, -7/16, 2447/5760, -959/2304, 238043/580608, -67223/165888, ...

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 293, Problem 11.
Steven R. Finch, Mathematical Constants, Cambridge, 2003, Section 1.3.1.

G. C. Greubel, Table of n, a(n) for n = 0..250
Markus Brede, On the convergence of the sequence defining Euler's number, Math. Intelligencer, 27, no. 3 (2005), 6-7.
Chao-Ping Chen and Junesang Choi, An Asymptotic Formula for (1+1/x)^x Based on the Partition Function, Amer. Math. Monthly 121 (2014), no. 4, 338--343. MR3183017.
Branko Malesevic, Yue Hu, and Cristinel Mortici, Accurate Estimates of (1+x)^{1/x} Involved in Carleman Inequality and Keller Limit, arXiv:1801.04963 [math.CA], 2018.

Cf. A094638, A130534, A055535 (denominators).
See also A239897/A239898.
Cf. A276977.

T:= proc(u) local k, l; add( Stirling1(u+k,k)*((u+k)!)^(-1)* add( (-1)^l/l!, l=0..u-k), k=0..u); end;

a[n_] := Sum[StirlingS1[n+k, k]/(n+k)!*Sum[(-1)^j/j!, {j, 0, n-k}], {k, 0, n}]; Table[a[n] // Numerator // Abs, {n, 0, 17}] (* Jean-François Alcover, Mar 04 2014, after Maple *)
Numerator[((1-x)^(-1/x)/E + O[x]^20)[[3]]] (* or *)
Numerator[Table[Sum[StirlingS1[n+k, k] Subfactorial[n-k] Binomial[2n, n+k], {k, 0, n}] (-1)^n/(2n)!, {n, 0, 10}]] (* Vladimir Reshetnikov, Sep 23 2016 *)

See Maple line for formula.

Edited by N. J. A. Sloane, Jul 01 2008 at the suggestion of R. J. Mathar

A239898 Bisection of A055535.

Original entry on oeis.org

1, 24, 5760, 580608, 1393459200, 73574645760, 24103053950976000, 578473294823424000, 9440684171518279680000, 271211974879377138647040000, 3579998068407778230140928000000, 282308419108727654719684608000000, 258955866680053703121272297226240000000

Offset: 0

N. J. A. Sloane, Apr 05 2014

Based on a very good approximation to e.

			Denominators of the fractions 1, 11/24, 2447/5760, 238043/580608, ... (see A055505/A055535).

Harlan J. Brothers and John A. Knox,, New closed-form approximations to the logarithmic constant e, Math. Intelligencer, 20 (1998), 25-29. MR1646709 (2000c:11209).
Chao-Ping Chen and Junesang Choi, An Asymptotic Formula for (1+1/x)^x Based on the Partition Function, Amer. Math. Monthly 121 (2014), no. 4, 338-343. MR3183017.
John A. Knox and Harlan J. Brothers, Novel series-based approximations to e, College Math. J. 30 (1999), no. 4, 269-275. MR1717867 (2000i:11198).

Cf. A055505/A055535, A239897 (numerators).

More terms from Amiram Eldar, May 08 2024

cp's OEIS Frontend

A055505 Numerators in expansion of (1-x)^(-1/x)/e.

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