The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A031523 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. 0

%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_

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 21 02:47 EDT 2023. Contains 365486 sequences. (Running on oeis4.)