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A009014
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Expansion of E.g.f.: (1 + x)/(1 + x + x^2/2).
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3
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1, 0, -1, 3, -6, 0, 90, -630, 2520, 0, -113400, 1247400, -7484400, 0, 681080400, -10216206000, 81729648000, 0, -12504636144000, 237588086736000, -2375880867360000, 0, 548828480360160000, -12623055048283680000
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OFFSET
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0,4
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LINKS
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FORMULA
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E.g.f.: (1+x)/(1+x+x^2/2) = 1/cosh(log(1+x)).
a(n) = -n*a(n-1)-n*(n-1)/2*a(n-2), a(0)=1, a(1)=0.
a(n) = -n!*(((-1+i)/2)^(n+1) + ((-1-i)/2)^(n+1)) = -n!/sqrt(2)^(n-1)*cos(3*Pi*(n+1)/4).
a(n) = 2*(-1)^n*int {t = 0..inf} t^n*exp(-t)*cos(t). (End)
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MAPLE
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seq(coeff(series(factorial(n)*((1+x)/(1+x+x^2/2)), x, n+1), x, n), n=0..25); # Muniru A Asiru, Jul 21 2018
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MATHEMATICA
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nn = 26; Range[0, nn]! CoefficientList[Series[1/Cosh[Log[1 + x]], {x, 0, nn}], x] (* T. D. Noe, Oct 05 2011 *)
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PROG
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(PARI) a(n)=-(2^-n)*n!*real((-1+I)^(n+1))
(PARI) x='x+O('x^30); Vec(serlaplace(1/cosh(log(1+x)))) \\ G. C. Greubel, Jul 21 2018
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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