A012736 sec(arctanh(x)*arctan(x)) = 1+12/4!*x^4+20048/8!*x^8+255870912/12!*x^12...

1, 12, 20048, 255870912, 12348478073088, 1607757077354376192, 462465118290965584465920, 257450488580368515571587072000, 252414780430562625969597955397713920

Offset

0,2

Links

Table of n, a(n) for n=0..8.

Mathematica

With[{nn=40}, Take[CoefficientList[Series[Sec[ArcTanh[x]ArcTan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 4}]] (* Harvey P. Dale, Aug 17 2016 *)

Crossrefs

Sequence in context: A159369 A175882 A216874 * A013750 A127395 A076807

Adjacent sequences: A012733 A012734 A012735 * A012737 A012738 A012739

Keyword

nonn

Author

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

Extensions

Definition clarified by Harvey P. Dale, Aug 17 2016

Status

approved