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A133631 a(n) = a(n-1) - 4*a(n-2), a(0)=1, a(1)=2. 1
1, 2, -2, -10, -2, 38, 46, -106, -290, 134, 1294, 758, -4418, -7450, 10222, 40022, -866, -160954, -157490, 486326, 1116286, -829018, -5294162, -1978090, 19198558, 27110918, -49683314, -158126986, 40606270, 673114214, 510689134, -2181767722, -4224524258 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..32.

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

FORMULA

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

a(n) = Sum_{k0..n} A133607(n,k)*2^k. - Philippe Deléham, Dec 29 2007

a(n) = (1/10)*i*sqrt(15)*(1/2 - (1/2)*i*sqrt(15))^n - (1/10)*i*sqrt(15)*(1/2 + (1/2)*i*sqrt(15))^n + (1/2)*(1/2 - (1/2)*i*sqrt(15))^n + (1/2)*(1/2 + (1/2)*i*sqrt(15))^n, with n >= 0 and i = sqrt(-1). - Paolo P. Lava, Nov 18 2008

CROSSREFS

Sequence in context: A038036 A297793 A319880 * A137450 A321415 A319692

Adjacent sequences:  A133628 A133629 A133630 * A133632 A133633 A133634

KEYWORD

easy,sign

AUTHOR

Philippe Deléham, Dec 28 2007

STATUS

approved

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Last modified November 27 18:22 EST 2020. Contains 338683 sequences. (Running on oeis4.)