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A109573 E.g.f.: 2*x/(1+exp(-2*x)). 1

%I

%S 0,1,2,0,-8,0,96,0,-2176,0,79360,0,-4245504,0,313155584,0,

%T -30460116992,0,3777576173568,0,-581777702256640,0,108932957168730112,

%U 0,-24370173276164456448,0,6419958484945407574016,0,-1967044844910430876860416,0,693575525634287935244206080,0

%N E.g.f.: 2*x/(1+exp(-2*x)).

%C (-1)^n*a(n) = 2^n*(2^n-1)*Bernoulli(n), n >= 1, are integers divisible by n. See the Koecher reference, p. 175, Satz, with a proof, and the J. Worpitzky and L. Kronecker JraM references 94 (1883) 203-232 and 268-269, respectively. - _Wolfdieter Lang_, Mar 09 2017

%D Max Koecher, Klassische elementare Analysis, Birkhäuser, Basel, Boston, 1987, p. 175

%H Indranil Ghosh, <a href="/A109573/b109573.txt">Table of n, a(n) for n = 0..332</a>

%F a(0) = 0 and for n > 0 a(n) = n 2^(n-1) E_{n-1}(1) where E_{m}(x) are the Euler polynomials. - _Peter Luschny_, Jan 26 2009

%F From _Sergei N. Gladkovskii_, Apr 04, Nov 23 and Dec 27 2013: (Start)

%F Continued fractions:

%F E.g.f.: 2*x/(Q(0)+1) where Q(k) = 1 - 2*x/(2*k+1 - x*(2*k+1)/(x - (k+1)/Q(k+1))).

%F E.g.f.: 1+2*x + T(0), where T(k) = 4*k-1 - x/(1 + x/( 4*k+1 - x/(1 + x/T(k+1)))).

%F E.g.f.: 1 + T(0), where T(k) = 4*k-1 + x/(1 - x/( 4*k+1 + x/(1 - x/T(k+1)))).

%F E.g.f.: x^2*E(0)+x, where E(k) = 1 - x^2/(x^2 + (2*k+1)*(2*k+3)/E(k+1)).

%F (End)

%F a(n) = (-1)^n*2^n*(2^n-1)*Bernoulli(n), with Bernoulli(n) = A027641(n)/A027642(n). For |a(n)| see the Koecher reference, p. 175, and a comment above. - _Wolfdieter Lang_, Mar 09 2017

%p G:=2*x/(1+exp(-2*x)): Gser:=series(G,x=0,35): 0,seq(n!*coeff(Gser,x^n),n=1..32); # yields the signed sequence

%p A109573 := n -> `if`(n = 0, 0, n*2^(n-1)*euler(n-1,1)): # _Peter Luschny_, Jan 26 2009

%t g[x_] = x/(-1 + Sum[(-2)^(n - 1)*x^n/n!, {n, 1, Infinity}]) h[x_, n_] = Dt[g[x], {x, n}] a[x_] = Table[h[x, n], {n, 0, 50}]; b = Abs[a[0]]

%t X[m_] := m Sum[(-2)^(m-1-k) k! StirlingS2[m-1,k], {k,0,m-1}]; Table[X[i],{i,0,20}] (* _Peter Luschny_, Apr 29 2009 *)

%o (PARI) for(n=0, 31, print1(n*sum(k=0, n-1, (-2)^(n - 1- k) * k! * stirling(n - 1, k, 2)), ", ")) \\ _Indranil Ghosh_, Mar 10 2017

%Y Cf. A027641, A027642.

%K sign,easy

%O 0,3

%A _Roger L. Bagula_, Jun 27 2005

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Last modified August 1 15:34 EDT 2021. Contains 346393 sequences. (Running on oeis4.)