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URL: https://oeis.org/A012464

⇱ A012464 - OEIS

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A012464
arctanh(arctan(x)*arctan(x))=2/2!*x^2-16/4!*x^4+608/6!*x^6-43776/8!*x^8...
0
0, 2, -16, 608, -43776, 5490432, -1043742720, 281302333440, -101944270848000, 47833801306275840, -28212954337286553600, 20432760600063600230400, -17826780360146975037849600, 18441699370235590444905922560
OFFSET
0,2
FORMULA
a(n) ~ (-1)^(n+1) * (2*n-1)! * ((exp(2)+1)/(exp(2)-1))^(2*n). - Vaclav Kotesovec, Feb 08 2015
MATHEMATICA
nn = 20; Table[(CoefficientList[Series[ArcTanh[ArcTan[x]^2], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Feb 08 2015 *)
CROSSREFS
Sequence in context: A060279 A369674 A012757 * A277036 A289202 A279324
KEYWORD
sign
EXTENSIONS
a(0)=0 prepended by Vaclav Kotesovec, Feb 08 2015
STATUS
approved