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A009125 Expansion of cosh(log(1+tan(x))). 1
1, 0, 1, -3, 20, -120, 976, -8568, 88640, -1011840, 12933376, -180964608, 2767631360, -45799004160, 816582578176, -15594628021248, 317710534983680, -6876762625966080, 157606194409701376, -3812723805066559488 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

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

FORMULA

a(n) ~ n! * (-1)^n * 4^n / Pi^(n+1). - Vaclav Kotesovec, Jan 22 2015

MATHEMATICA

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

CoefficientList[Series[(1 + (1 + Tan[x])^2)/(2*(1 + Tan[x])), {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 22 2015 *)

CROSSREFS

Sequence in context: A037788 A037669 A228066 * A037795 A228750 A187442

Adjacent sequences:  A009122 A009123 A009124 * A009126 A009127 A009128

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 4 23:10 EST 2016. Contains 278755 sequences.