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Search: id:A121720
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| A121720 |
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a(n)= 4*a(n-2) -2*a(n-4). |
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+0
1
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| 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
(list; graph; listen)
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OFFSET
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1,4
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FORMULA
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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 (ppl(AT)spl.at), Nov 02 2009]
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MATHEMATICA
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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}]
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CROSSREFS
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Cf A002530, A048788.
Sequence in context: A025084 A134512 A106523 this_sequence A007068 A056515 A056516
Adjacent sequences: A121717 A121718 A121719 this_sequence A121721 A121722 A121723
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KEYWORD
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nonn,easy,new
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AUTHOR
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Roger Bagula and Gary Adamson (rlbagulatftn(AT)yahoo.com), Sep 07 2006
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EXTENSIONS
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Definition replaced by recurrence - The Assoc. Editors of the OEIS, Oct 14 2009
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