A031619 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 31.

6109, 12149, 19681, 20530, 30397, 40973, 55921, 57346, 70514, 71578, 73189, 87977, 89165, 91565, 110665, 111997, 128693, 132298, 133754, 151169, 151946, 155861, 157441, 159029, 159826, 178813, 203341, 206957, 212441, 234250, 235217, 236186, 237157, 238130

Offset

1,1

Links

Table of n, a(n) for n=1..34.

Mathematica

cf31Q[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]] == 31]; Select[Range[250000], cf31Q] (* Harvey P. Dale, Jun 01 2018 *)

Crossrefs

Sequence in context: A211929 A251994 A201225 * A235764 A235547 A345186

Adjacent sequences: A031616 A031617 A031618 * A031620 A031621 A031622

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected and extended by Harvey P. Dale, Jun 01 2018

Status

approved