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A205572
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E.g.f.: 1/(cos(x) - sinh(x)).
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1
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1, 1, 3, 13, 73, 521, 4443, 44213, 502993, 6436561, 91520883, 1431459613, 24424457113, 451474855001, 8987248462923, 191682800678213, 4360821252342433, 105410131831623841, 2697863748098734563, 72885101748061044013, 2072687894252786558953
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OFFSET
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0,3
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COMMENTS
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Radius of convergence of e.g.f. is |x| < r where r = 0.703290658863965... satisfies cos(r) = sinh(r).
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LINKS
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FORMULA
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a(2^n + k) == a(k) (mod 2^n) for k>=0, n>=1 (conjecture).
E.g.f.: E(x) = 1/(cos(x) - sinh(x)) = 1/G(0) where G(k)= 1 -x/(4*k +1 - x*(4*k +1)/(4*k + 2 + x - 2*x*(2*k+1)/(4*k + 3 + x- x*(4*k+3)/(x -4*(k+1)/G(k+1))))); Radius of convergence of e.g.f.E(x)=1/G(0) is infinity; (continued fraction, 3rd kind, 5-step). - Sergei N. Gladkovskii, Jun 08 2012, Oct 03 2012
a(n) ~ n! * 2*exp(r)/((2*sin(r)*exp(r)+exp(2*r)+1)*r^(n+1)), where r = 0.7032906588639654... is defined in the comment. - Vaclav Kotesovec, Sep 22 2013
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EXAMPLE
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E.g.f.: A(x) = 1 + x + 3*x^2/2! + 13*x^3/3! + 73*x^4/4! + 521*x^5/5! +...
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MATHEMATICA
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CoefficientList[Series[1/(Cos[x]-Sinh[x]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Sep 22 2013 *)
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PROG
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(PARI) {a(n)=n!*polcoeff(1/(cos(x+x*O(x^n)) - sinh(x+x*O(x^n))), n)}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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