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A122112 a(0)=1, a(1)=-2, a(n)=4*a(n-2)-a(n-1) for n>1. 0
1, -2, 6, -14, 38, -94, 246, -622, 1606, -4094, 10518, -26894, 68966, -176542, 452406, -1158574, 2968198, -7602494, 19475286, -49885262, 127786406, -327327454, 838473078, -2147782894, 5501675206, -14092806782, 36099507606, -92470734734 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..27.

Index entries for linear recurrences with constant coefficients, signature (-1,4).

FORMULA

a(n) = (-1)^n * A026597(n). a(n) = Sum_[k, 0<=k<=n} (-2)^(n-k) * A055830(n,k).

G.f.: (1-x)/(1+x-4*x^2).

a(n) = (1/2) * [(-1/2) - (1/2)*sqrt(17)]^n + (3/34) * [(-1/2) - (1/2)*sqrt(17)]^n * sqrt(17) - (3/34) * sqrt(17) * [(-1 /2) + (1/2)*sqrt(17)]^n + (1/2) * [(-1/2) + (1/2)*sqrt(17)]^n, with n>=0 [From Paolo P. Lava, Nov 19 2008]

CROSSREFS

Sequence in context: A263758 A100067 A026597 * A190788 A168259 A275208

Adjacent sequences:  A122109 A122110 A122111 * A122113 A122114 A122115

KEYWORD

sign

AUTHOR

Philippe Deléham, Oct 18 2006

EXTENSIONS

Corrected by T. D. Noe, Nov 07 2006

STATUS

approved

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Last modified January 15 20:47 EST 2019. Contains 319184 sequences. (Running on oeis4.)