A031649 Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 61.

23741, 75706, 77365, 113017, 115721, 158573, 160169, 161773, 212746, 215521, 270689, 275914, 336761, 339085, 343757, 493333, 582794, 584321, 587381, 595066, 598154, 599701, 689629, 692953, 785837, 789385, 792941, 800077, 909170, 911077, 914897

Offset

1,1

Links

Table of n, a(n) for n=1..31.

Mathematica

cf61Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 61]; Select[Range[920000], cf61Q] (* Harvey P. Dale, Apr 25 2019 *)

Crossrefs

Sequence in context: A179918 A168169 A344377 * A011254 A226002 A066234

Adjacent sequences: A031646 A031647 A031648 * A031650 A031651 A031652

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected and extended by Harvey P. Dale, Apr 25 2019

Status

approved