A031656 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 68.

29609, 57649, 94330, 94945, 96181, 141497, 143005, 262369, 336689, 420265, 422861, 425465, 515965, 521725, 524617, 621473, 724826, 728234, 729941, 733361, 735074, 738506, 743669, 847129, 850813, 988877, 992857, 1113986, 1118210

Offset

1,1

Links

Table of n, a(n) for n=1..29.

Mathematica

cf68Q[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]] == 68]; Select[Range[1200, 112*10^4], cf68Q] (* Harvey P. Dale, Jan 27 2020 *)

Crossrefs

Sequence in context: A251563 A022200 A234669 * A236734 A236317 A204601

Adjacent sequences: A031653 A031654 A031655 * A031657 A031658 A031659

Keyword

nonn

Author

David W. Wilson

Extensions

First term 4625 removed by Georg Fischer, Jun 16 2019

Definition modified by Harvey P. Dale, Jan 27 2020

Status

approved