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A009081 E.g.f. is cos(tan(x)/cos(x)), coefficients of even powers of x. 1
1, -1, -19, -517, -18023, -587529, 19183749, 12219870323, 3379214470193, 883981857320943, 238930492488456221, 66829754023676225259, 18410558239851140719561, 4167711609283156286652647, -82954815883633697917244747, -1284116651310135986426544039581 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

All coefficients of odd powers of x are zero.

LINKS

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

MATHEMATICA

With[{nn=30}, Take[CoefficientList[Series[Cos[Tan[x]/Cos[x]], {x, 0, nn}], x]Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jan 28 2012 *)

PROG

(PARI)

x='x+O('x^66);  /* that many terms */

v=Vec(serlaplace(cos(tan(x)/cos(x))));

vector(#v\2, j, v[2*j-1])  /* show terms */

/* Joerg Arndt, Jan 28 2012 */

CROSSREFS

Sequence in context: A201711 A243784 A158583 * A057644 A283382 A196512

Adjacent sequences:  A009078 A009079 A009080 * A009082 A009083 A009084

KEYWORD

sign

AUTHOR

R. H. Hardin

EXTENSIONS

Extended with signs by Olivier Gérard, Mar 15 1997

STATUS

approved

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Last modified May 18 12:45 EDT 2021. Contains 343995 sequences. (Running on oeis4.)