A031611 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 23.

3389, 6938, 10897, 11317, 11530, 17021, 22669, 30154, 31909, 40289, 41498, 48761, 49645, 51437, 59005, 72353, 74513, 76154, 83569, 85306, 85889, 86474, 87061, 88241, 90026, 96829, 104413, 112397, 115085, 120557, 128410, 129125, 131282

Offset

1,1

Links

Table of n, a(n) for n=1..33.

Mathematica

cf23Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {0, 0}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 23]; Select[Range[132000], cf23Q] (* Harvey P. Dale, Dec 13 2019 *)

Crossrefs

Sequence in context: A153746 A243217 A133965 * A133966 A043671 A262176

Adjacent sequences: A031608 A031609 A031610 * A031612 A031613 A031614

Keyword

nonn

Author

David W. Wilson

Extensions

First term 530 removed by Georg Fischer, Jun 16 2019

Status

approved