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A012007 cosh(log(cos(x))) = 1+3/4!*x^4+30/6!*x^6+693/8!*x^8+25260/10!*x^10... 4
1, 0, 3, 30, 693, 25260, 1351383, 99680490, 9695756073, 1202439837720, 185185594118763, 34674437196568950, 7757267081778543453, 2043536254646561946180, 626129820701814932734143, 220771946624511552276841410, 88759695789769644718332394833 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..16.

FORMULA

a(n) = (1/2)*((-1)^n+A000364(n)). Also cosh(log(cos(x))) = 1/2*(cos(x)+1/cos(x)) is the reciprocal of the e.g.f. of A012009. - Peter Bala, Dec 02 2011

MATHEMATICA

terms = 15; s = Cosh[Log[Cos[x]]] + O[x]^(2*terms); CoefficientList[s, x^2] * Table[(2n)!, {n, 0, terms-1}] (* Jean-Fran├žois Alcover, May 22 2017 *)

CROSSREFS

Cf. A012003, A012008, A012009.

Sequence in context: A007019 A186941 A082879 * A065753 A255926 A113677

Adjacent sequences:  A012004 A012005 A012006 * A012008 A012009 A012010

KEYWORD

nonn

AUTHOR

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

EXTENSIONS

Confirmed by N. J. A. Sloane, Dec 17 2011

STATUS

approved

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Last modified February 20 12:33 EST 2018. Contains 299379 sequences. (Running on oeis4.)