A031566 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 68.

4626, 4642, 4678, 4694, 4702, 4722, 4726, 4742, 4766, 4786, 4798, 4802, 4806, 4818, 4822, 4834, 4838, 4846, 4854, 4866, 4882, 4894, 4898, 10407, 10446, 10452, 10473, 10479, 10497, 10524, 10533, 10551, 10569, 10581, 10587, 10596, 10617, 10623, 10641

Offset

1,1

Links

Table of n, a(n) for n=1..39.

Mathematica

cf68Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]]==68]; Select[Range[11000], cf68Q] (* Harvey P. Dale, Jan 10 2019 *)

Crossrefs

Sequence in context: A358445 A254850 A139410 * A236815 A343637 A233855

Adjacent sequences: A031563 A031564 A031565 * A031567 A031568 A031569

Keyword

nonn

Author

David W. Wilson

Status

approved