%I #17 Aug 17 2021 23:48:27
%S 627,631,643,647,659,679,683,691,699,719,727,2504,2536,2560,2656,2688,
%T 2720,2752,2784,2792,2816,2912,5631,5703,5835,5847,5919,5991,6051,
%U 6207,6339,6351,6423,6495,6555,10008,10072,10264,10328,10376,10456,10648
%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 25.
%C "Central term" means the term at 1/2 the length of the period.  _Harvey P. Dale_, Dec 27 2011
%t cfevQ[n_]:=Module[{sr=Sqrt[n],cf,tr,len},cf=ContinuedFraction[sr];tr = !IntegerQ[sr];len=If[tr,Length[cf[[2]]],1];tr&&EvenQ[len]&&cf[[2]][[len/2]]==25]; Select[Range[11000],cfevQ2] (* _Harvey P. Dale_, Dec 27 2011 *)
%K nonn
%O 1,1
%A _David W. Wilson_
