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A133186 Period 4: repeat [1, 2, 1, -4]. 0
1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4, 1, 2, 1, -4 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..75.

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

FORMULA

a(n) = (1/4)*{-5*(n mod 4)+5*[(n+1) mod 4]+[(n+2) mod 4]-[(n+3) mod 4]}. - Paolo P. Lava, Oct 24 2007

a(n) = -[(3/2)*I]*I^n+(-1)^n+[(3/2)*I]*(-I)^n. - Paolo P. Lava, Jul 17 2008

G.f.: 1/(1+x)+3x/(1+x^2). a(n) = (-1)^n+3*A056594(n-1). [R. J. Mathar, Oct 30 2008]

From Wesley Ivan Hurt, Jul 09 2016: (Start)

a(n) + a(n-1) + a(n-2) + a(n-3) = 0 for n>2, a(n) = a(n-4) for n>3.

a(n) = cos(n*Pi) + 3*sin(n*Pi/2). (End)

MAPLE

seq(op([1, 2, 1, -4]), n=0..40); # Wesley Ivan Hurt, Jul 09 2016

MATHEMATICA

PadRight[{}, 100, {1, 2, 1, -4}] (* Wesley Ivan Hurt, Jul 09 2016 *)

PROG

(MAGMA) &cat [[1, 2, 1, -4]^^30]; // Wesley Ivan Hurt, Jul 09 2016

CROSSREFS

Cf. A056594, A109008.

Sequence in context: A057550 A324892 A059150 * A084236 A068057 A335852

Adjacent sequences:  A133183 A133184 A133185 * A133187 A133188 A133189

KEYWORD

sign,easy

AUTHOR

Paul Curtz, Oct 07 2007

STATUS

approved

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Last modified July 16 13:35 EDT 2020. Contains 335788 sequences. (Running on oeis4.)