A012811 cosh(sec(x)*arctan(x))=1+1/2!*x^2+5/4!*x^4+205/6!*x^6+2473/8!*x^8...

1, 1, 5, 205, 2473, 475385, -2814227, 5900398725, -532397600303, 273302104270705, -68724093821987755, 35776180280496600509, -16339748046588020242311, 10552119508350355540652905

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Cosh[Sec[x]ArcTan[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jan 31 2026 *)

Crossrefs

Sequence in context: A157389 A128678 A232987 * A186722 A060486 A002438

Adjacent sequences: A012808 A012809 A012810 * A012812 A012813 A012814

Keyword

sign

Author

Patrick Demichel

Status

approved