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 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
 627, 631, 643, 647, 659, 679, 683, 691, 699, 719, 727, 2504, 2536, 2560, 2656, 2688, 2720, 2752, 2784, 2792, 2816, 2912, 5631, 5703, 5835, 5847, 5919, 5991, 6051, 6207, 6339, 6351, 6423, 6495, 6555, 10008, 10072, 10264, 10328, 10376, 10456, 10648 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS "Central term" means the term at 1/2 the length of the period. - Harvey P. Dale, Dec 27 2011 LINKS Table of n, a(n) for n=1..42. MATHEMATICA 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 *) CROSSREFS Sequence in context: A031728 A031638 A098262 * A345523 A345777 A129974 Adjacent sequences: A031520 A031521 A031522 * A031524 A031525 A031526 KEYWORD nonn AUTHOR David W. Wilson STATUS approved

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Last modified June 4 21:13 EDT 2023. Contains 363130 sequences. (Running on oeis4.)