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A031516
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that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 18.
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0
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326, 334, 354, 358, 374, 382, 386, 398, 732, 741, 753, 789, 804, 813, 831, 849, 897, 1300, 1324, 1340, 1348, 1356, 1372, 1388, 1396, 1412, 1436, 1452, 1460, 1468, 1492, 1500, 1516, 1532, 1548, 1556, 1564, 1588, 1596, 2030, 2045, 2095, 2105, 2155, 2195
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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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cf18Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 18]; Select[Range[2200], cf18Q] (* Harvey P. Dale, May 26 2018 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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