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A013209
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Expansion of e.g.f. log(sech(x) + arctanh(x)).
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0
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0, 1, -2, 7, -24, 173, -1280, 11779, -120960, 1474969, -19695232, 296068991, -4847011840, 87094091589, -1687646744576, 35308668668155, -789939274514432, 18872654969343537, -478658276989173760
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OFFSET
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1,3
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LINKS
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FORMULA
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E.g.f.: log(sech(x)+arctanh(x)).
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EXAMPLE
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x - 2/2!*x^2 + 7/3!*x^3 - 24/4!*x^4 + 173/5!*x^5 ...
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PROG
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(PARI) a(n)=local(y); if(n<0, 0, y=x+x*O(x^n); n!*polcoeff(log(1/cosh(y)+atanh(y)), n))
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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Patrick Demichel (patrick.demichel(AT)hp.com)
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EXTENSIONS
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STATUS
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approved
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