A031570 Numbers k such 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 72.

5186, 5198, 5218, 5282, 5286, 5294, 5298, 5302, 5314, 5318, 5326, 5342, 5346, 5366, 5374, 5378, 5398, 5414, 5422, 5438, 5442, 5462, 5474, 11667, 11721, 11733, 11757, 11769, 11793, 11811, 11814, 11829, 11841, 11892, 11901, 11964, 11973, 11991, 12009

Offset

1,1

Links

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

Mathematica

cf72Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 72]; Select[Range[12100], cf72Q] (* Harvey P. Dale, Mar 24 2022 *)

Crossrefs

Sequence in context: A061050 A175745 A190464 * A066167 A247265 A252050

Adjacent sequences: A031567 A031568 A031569 * A031571 A031572 A031573

Keyword

nonn

Author

David W. Wilson

Status

approved