%I #12 Aug 17 2021 23:48:27
%S 2211,2227,2231,2239,2243,2251,2263,2267,2283,2287,2311,2339,2347,
%T 2351,2363,2371,2383,2399,8840,8864,8872,8896,8936,8960,9032,9056,
%U 9088,9160,9256,9320,9344,9376,9440,9448,9472,9512,9536,9600,19887,19959,20031
%N 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.
%t 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 *)
%K nonn
%O 1,1
%A _David W. Wilson_
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