OFFSET
0,6
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..486
FORMULA
G.f.: x/(x^2-1)*(T(0)*(1+x)/(1+2*x) -2), where T(k) = 1 - x^2*(k+1)^2/(x^2*(k+1)^2 + (1+2*x)^2/T(k+1)); (continued fraction). - Sergei N. Gladkovskii, Nov 11 2013
a(n) = Sum_{k=0..floor((n-1)/2)} A028296(k). - Daniel Suteu, Nov 16 2018
a(n) = Sum_{k=0..n-1} E(k), where E(k) = A122045(k). - Amiram Eldar and Thomas Ordowski, Feb 06 2020
MAPLE
seq(add(euler(k), k=0..n-1), n=0..24); # Peter Luschny, Feb 06 2020
MATHEMATICA
With[{nmax = 30}, CoefficientList[Series[Log[1 + Tanh[x]]*Exp[x], {x, 0, nmax}], x]*Range[0, nmax]!] (* G. C. Greubel, Nov 16 2018 *)
PROG
(PARI) a(n) = sum(k=0, floor((n-1)/2), 2*imag(polylog(-2*k, I))); \\ Daniel Suteu, Nov 16 2018
(PARI) x='x+O('x^30); concat([0], Vec(serlaplace(log(1+tanh(x))*exp(x)))) \\ G. C. Greubel, Nov 16 2018
(Magma) m:=30; R<x>:=PowerSeriesRing(Rationals(), m); b:=Coefficients(R!( Exp(x)*Log(1 + Tanh(x)))); [0] cat [Factorial(n)*b[n]: n in [1..(m-1)]]; // G. C. Greubel, Nov 16 2018
CROSSREFS
KEYWORD
sign,easy
AUTHOR
EXTENSIONS
Extended with signs by Olivier Gérard, Mar 15 1997
STATUS
approved