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A009381 Expansion of log(1+tan(x)/cosh(x)). 0
0, 1, -1, 1, -2, 25, -136, 761, -4752, 42065, -386176, 3898321, -42551552, 521329705, -6816879616, 96017526281, -1446339889152, 23356125062945, -399659935891456, 7240133620964641, -138393644469911552, 2786977252450841785 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 5 13:38 EST 2016. Contains 278768 sequences.