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Search: id:A050512
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| A050512 |
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a(n)=(a(n-1)a(n-3)-a(n-2)^2)/a(n-4), a(1)=a(2)=a(3)=1, a(4)=-1. |
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+0
4
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| 0, 1, 1, 1, -1, -2, -3, -1, 7, 11, 20, -19, -87, -191, -197, 1018, 2681, 8191, -5841, -81289, -261080, -620551, 3033521, 14480129, 69664119, -2664458, -1612539083, -7758440129, -37029252553, 181003520899, 1721180313660
(list; graph; listen)
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OFFSET
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0,6
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FORMULA
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a(2n+1)=a(n+2)a(n)^3 - a(n-1)a(n+1)^3, a(2n)=a(n+2)a(n)a(n-1)^2 - a(n)a(n-2)a(n+1)^2.
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PROGRAM
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(PARI) an=vector(200); for(n=1, 4, an[ n ]=[ 1, 1, 1, -1 ][ n ]); for(n=5, length(an), an[ n ]=(an[ n-1 ]*an[ n-3 ]-an[ n-2 ]^2)/an[ n-4 ]); a(n) =sign(n)*an[ abs(n)+(n==0) ]
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CROSSREFS
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Cf. A006769.
Sequence in context: A121637 A161847 A101175 this_sequence A107102 A103364 A104027
Adjacent sequences: A050509 A050510 A050511 this_sequence A050513 A050514 A050515
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KEYWORD
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sign,easy,nice
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AUTHOR
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Michael Somos
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