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A167199 First column of A167196. 2
1, -2, 7, -36, 246, -2100, 21510, -257040, 3510360, -53933040, 920694600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Limiting ratio 2+n*a(n-1)/a(n) converges to A002193.

LINKS

Table of n, a(n) for n=0..10.

FORMULA

Conjecture: E.g.f.: 2/(2+4*x+x^2) = G(0)/(1+x) where  G(k) = 1 - x/((1+x) - x*(1+x)/(x - (1+x)*2/G(k+1) )); (recursively defined continued fraction). - Sergei N. Gladkovskii, Dec 28 2012.

a(n) ~ n! * (-1)^n * (1+sqrt(2))/2 * (1+1/sqrt(2))^n. - Vaclav Kotesovec, Oct 08 2013

MATHEMATICA

CoefficientList[Series[2/(2+4*x+x^2), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Oct 08 2013 *)

CROSSREFS

Cf. A167196, A002193.

Sequence in context: A095793 A029768 A180271 * A007889 A125033 A034430

Adjacent sequences:  A167196 A167197 A167198 * A167200 A167201 A167202

KEYWORD

more,sign

AUTHOR

Mats Granvik, Oct 30 2009

STATUS

approved

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Last modified February 20 08:12 EST 2018. Contains 299368 sequences. (Running on oeis4.)