A031668 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 80.

40829, 132577, 195485, 197257, 362629, 365041, 466778, 473633, 584057, 587117, 590185, 850613, 852458, 1002626, 1006634, 1014674, 1016689, 1018706, 1024769, 1184473, 1188829, 1351085, 1360397, 1365065, 1374425, 1541042, 1548497

Offset

1,1

Links

Table of n, a(n) for n=1..27.

Mathematica

cf80Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {0, 0}, ContinuedFraction[s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[Floor[len/2]]]==cf[[Ceiling[len/2]]]==80]; Select[Range[155*10^4], cf80Q] (* Harvey P. Dale, Jul 24 2022 *)

Crossrefs

Subsequence of A003814.

Sequence in context: A097238 A249879 A046180 * A164648 A232301 A212080

Adjacent sequences: A031665 A031666 A031667 * A031669 A031670 A031671

Keyword

nonn

Author

David W. Wilson

Extensions

First term 6401 removed by Georg Fischer, Jun 16 2019

Status

approved