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%I #12 Aug 17 2021 23:48:27
%S 7571,7583,7587,7591,7603,7607,7611,7619,7639,7643,7667,7679,7687,
%T 7691,7699,7703,7723,7727,7731,7751,7759,7771,7803,7811,7823,7827,
%U 7831,7867,7879,7883,7899,7903,7907,7919,30280,30304,30336,30368,30376,30400,30432
%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 87.
%t cf87Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{1}, ContinuedFraction[ s][[2]]];len=Length[cf];EvenQ[len]&&cf[[len/2]] == 87]; Select[Range[31000],cf87Q] (* _Harvey P. Dale_, Jan 24 2019 *)
%K nonn
%O 1,1
%A _David W. Wilson_
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