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A012001 E.g.f.: -tan(log(cos(x))), even powers only. 1
0, 1, 2, 46, 1112, 55816, 3804272, 372397936, 47682319232, 7841034902656, 1601250315636992, 398250217200414976, 118406090377889303552, 41478295178427681104896, 16904918898000336224294912 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

The highest power of 2 dividing a(n) appears to be A011371(n). The odd part starts 1, 1, 23, 139, 6977, 237767, 23274871, 372518119, 61258085177,.... - Ralf Stephan, Aug 14 2013

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..235

EXAMPLE

-tan(log(cos(x))) = 1/2!*x^2 + 2/4!*x^4 + 46/6!*x^6 + 1112/8!*x^8 + ...

MATHEMATICA

With[{nn = 50}, Take[CoefficientList[Series[-Tan[Log[Cos[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* G. C. Greubel, Apr 12 2017 *)

PROG

(PARI) a(n)={n*=2; my(x='x+O('x^(n+1))); polcoeff( serlaplace( -tan(log(cos(x)))), n); } \\ Ralf Stephan, Aug 14 2013

CROSSREFS

Sequence in context: A174592 A066555 A290046 * A012006 A279524 A264500

Adjacent sequences:  A011998 A011999 A012000 * A012002 A012003 A012004

KEYWORD

nonn

AUTHOR

Patrick Demichel (patrick.demichel(AT)hp.com)

EXTENSIONS

Checked by N. J. A. Sloane, Dec 16 2011

STATUS

approved

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Last modified November 20 00:42 EST 2017. Contains 294957 sequences.