A009366 - OEIS

A009366

Expansion of log(1+tan(tan(x))).

0, 1, -1, 6, -22, 176, -1192, 12240, -122288, 1561088, -20588544, 318007808, -5193155328, 94807748608, -1841205505024, 38942692972544, -875204314126336, 21088169713729536, -537861879179575296, 14558790290337431552

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..19.

FORMULA

a(n) ~ (n-1)! * (-1)^(n+1) / (arctan(Pi/4))^n. - Vaclav Kotesovec, Jan 23 2015

MATHEMATICA

Log[ 1+Tan[ Tan[ x ] ] ]

CoefficientList[Series[Log[1 + Tan[Tan[x]]], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 23 2015 *)

CROSSREFS

Sequence in context: A000993 A028406 A090372 * A230964 A075811 A302926

Adjacent sequences: A009363 A009364 A009365 * A009367 A009368 A009369

KEYWORD

sign,easy

AUTHOR

R. H. Hardin

EXTENSIONS

Extended with signs by Olivier Gérard, Mar 15 1997

STATUS

approved