A009391 Expansion of log(1 + tanh(x))/cos(x).

0, 1, -1, 3, -4, 25, -61, 427, -1184, 12465, -49201, 555731, -2361844, 35135945, -191422141, 2990414715, -17147588384, 329655706465, -2289437638081, 45692713833379, -329955144475204, 7777794952988025, -65643617893832221

Offset

0,4

Links

Table of n, a(n) for n=0..22.

Formula

a(n) ~ n! * 2^(n+1) * (Pi + (1+(-1)^n) * log(2/(1+exp(Pi)))) / Pi^(n+1). - Vaclav Kotesovec, Jan 24 2015

Mathematica

CoefficientList[Series[Log[1 + Tanh[x]]*Sec[x], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 24 2015 *)

Crossrefs

a(2n+1) = A009843(n), |a(2n)| = A009391(2n).

Sequence in context: A338425 A304210 A245244 * A212696 A192346 A335739

Adjacent sequences: A009388 A009389 A009390 * A009392 A009393 A009394

Keyword

sign,easy

Author

R. H. Hardin

Extensions

Extended with signs by Olivier Gérard, Mar 15 1997

Incorrect Mathematica program deleted by Harvey P. Dale, Oct 14 2022

Status

approved