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A031545
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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 47.
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0
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2211, 2227, 2231, 2239, 2243, 2251, 2263, 2267, 2283, 2287, 2311, 2339, 2347, 2351, 2363, 2371, 2383, 2399, 8840, 8864, 8872, 8896, 8936, 8960, 9032, 9056, 9088, 9160, 9256, 9320, 9344, 9376, 9440, 9448, 9472, 9512, 9536, 9600, 19887, 19959, 20031
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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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cf47Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s] [[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 47]; Select[Range[21000], cf47Q] (* Harvey P. Dale, Apr 07 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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