A009381 Expansion of log(1+tan(x)/cosh(x)).

0, 1, -1, 1, -2, 25, -136, 761, -4752, 42065, -386176, 3898321, -42551552, 521329705, -6816879616, 96017526281, -1446339889152, 23356125062945, -399659935891456, 7240133620964641, -138393644469911552, 2786977252450841785

Offset

0,5

Links

Table of n, a(n) for n=0..21.

Formula

a(n) ~ (n-1)! * (-1)^(n+1) / r^n, where r = 0.99355002995970290924151689720077885406082615338... is the root of the equation cosh(r) = tan(r). - Vaclav Kotesovec, Jan 24 2015

Mathematica

Log[ 1+Tan[ x ]/Cosh[ x ] ]
CoefficientList[Series[Log[1 + Sech[x]*Tan[x]], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 24 2015 *)

Crossrefs

Sequence in context: A196011 A080515 A258943 * A063264 A024533 A220276

Adjacent sequences: A009378 A009379 A009380 * A009382 A009383 A009384

Keyword

sign,easy

Author

R. H. Hardin

Extensions

Extended with signs by Olivier Gérard, Mar 15 1997

Status

approved