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A121720 a(n)= 4*a(n-2) -2*a(n-4). 0
0, 1, 1, 3, 4, 10, 14, 34, 48, 116, 164, 396, 560, 1352, 1912, 4616, 6528, 15760, 22288, 53808, 76096, 183712, 259808, 627232, 887040, 2141504, 3028544, 7311552, 10340096, 24963200, 35303296, 85229696, 120532992, 290992384, 411525376, 993510144, 1405035520 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..37.

Index entries for linear recurrences with constant coefficients, signature (0, 4, 0, -2).

FORMULA

a(n) = A007068(n-2), n>2.

G.f.: -x^2*(-1-x+x^2)/(1-4*x^2+2*x^4). [Oct 14 2009]

a(n)=(1/4)*(2-sqrt(2))^(1/2*n)*(2-sqrt(2))^(1/4*(-1)^n)*(2-sqrt(2))^(-1/4)*(1-sqrt(2)-(-1)^n)+(1/4)*(2 +sqrt(2))^(-1/4)*(2+sqrt(2))^(1/2*n)*(2+sqrt(2))^(1/4*(-1)^n)*(1+sqrt(2)-(-1)^n), with n>=0 [From Paolo P. Lava, Nov 02 2009]

MATHEMATICA

f[n_] := 1 + Mod[n, 2] M[n_] := {{0, 1}, {f[n], 1}} v[1] = {0, 1} v[n_] := v[n] = M[n].v[n - 1] a = Table[v[n][[1]], {n, 1, 30}]

LinearRecurrence[{0, 4, 0, -2}, {0, 1, 1, 3}, 30] (* Harvey P. Dale, May 21 2014 *)

CROSSREFS

Cf A002530, A048788.

Sequence in context: A134512 A106523 A007068 * A056515 A056516 A056517

Adjacent sequences:  A121717 A121718 A121719 * A121721 A121722 A121723

KEYWORD

nonn,easy

AUTHOR

Roger L. Bagula and Gary W. Adamson, Sep 07 2006

EXTENSIONS

Definition replaced by recurrence - The Assoc. Editors of the OEIS, Oct 14 2009

More terms from Harvey P. Dale, May 21 2014

STATUS

approved

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Last modified August 20 22:45 EDT 2019. Contains 326155 sequences. (Running on oeis4.)