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A105426
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a(0)=1, a(1)=5, a(n)=8*a(n-1)-a(n-2).
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3
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1, 5, 39, 307, 2417, 19029, 149815, 1179491, 9286113, 73109413, 575589191, 4531604115, 35677243729, 280886345717, 2211413522007, 17410421830339, 137071961120705, 1079165267135301, 8496250175961703, 66890836140558323
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OFFSET
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0,2
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COMMENTS
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15*a(n)^2-14 is a square for all n.
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LINKS
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FORMULA
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G.f.: (1-3x)/(1-8x+x^2). a(n)=2*A105045(2*n+1)-1. a(-n)=2*A105045(2*n)-1, if n>0.
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MATHEMATICA
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LinearRecurrence[{8, -1}, {1, 5}, 20] (* Harvey P. Dale, Feb 25 2016 *)
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PROG
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(PARI) a(n)=subst(19*poltchebi(n)-poltchebi(n-1), x, 4)/15
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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