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A013180 sec(arctanh(x)+arctan(x))=1+4/2!*x^2+80/4!*x^4+4480/6!*x^6... 0
1, 4, 80, 4480, 462080, 77248000, 18902835200, 6385348403200, 2843287396352000, 1614575957622784000, 1138477316012441600000, 976037590707833405440000, 999765439694232249958400000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..12.

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Sec[ArcTanh[x]+ArcTan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Ray Chandler, Nov 29 2016 *)

CROSSREFS

Sequence in context: A013139 A013007 A013008 * A322751 A000316 A012106

Adjacent sequences:  A013177 A013178 A013179 * A013181 A013182 A013183

KEYWORD

nonn

AUTHOR

Patrick Demichel (patrick.demichel(AT)hp.com)

STATUS

approved

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Last modified January 25 18:25 EST 2022. Contains 350572 sequences. (Running on oeis4.)