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A156677
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a(n) = 81n^2 - 118n + 43.
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5
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43, 6, 131, 418, 867, 1478, 2251, 3186, 4283, 5542, 6963, 8546, 10291, 12198, 14267, 16498, 18891, 21446, 24163, 27042, 30083, 33286, 36651, 40178, 43867, 47718, 51731, 55906, 60243, 64742, 69403, 74226, 79211, 84358, 89667, 95138, 100771
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OFFSET
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0,1
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COMMENTS
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The identity (6561*n^2-9558*n+3482)^2-(81*n^2-118*n+43)*(729*n-531)^2=1 can be written as A156773(n)^2-a(n)*A156771(n)^2=1 for n>0.
For n >= 1, the continued fraction expansion of sqrt(a(n)) is [9n-7; {2, 4, 9n-7, 4, 2, 18n-14}]. For n=1, this collapses to [2; {2, 4}]. - Magus K. Chu, Sep 09 2022
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LINKS
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FORMULA
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a(n) = 3*a(n-1) -3*a(n-2) +a(n-3).
G.f.: (-43+123*x-242*x^2)/(x-1)^3.
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MATHEMATICA
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LinearRecurrence[{3, -3, 1}, {43, 6, 131}, 40]
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PROG
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(Magma) I:=[43, 6, 131]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]];
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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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EXTENSIONS
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STATUS
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approved
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