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A031631
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Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 43.
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0
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11689, 23458, 37717, 38890, 56765, 78569, 79693, 106501, 138673, 139418, 171757, 204745, 210205, 212041, 248533, 252533, 255554, 290069, 291146, 293306, 294389, 295474, 296561, 298741, 299834, 300929, 302026, 395225, 402797, 405337
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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cf43Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 43]; Select[Range[406000], cf43Q] (* Harvey P. Dale, Aug 25 2019 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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