A009391 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

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

(list; graph; refs; listen; history; text; internal format)

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