A031568 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 70.

4902, 4918, 4934, 4942, 4946, 4962, 4978, 4994, 5006, 5026, 5058, 5062, 5074, 5078, 5086, 5094, 5102, 5126, 5142, 5154, 5158, 5182, 11028, 11037, 11073, 11091, 11121, 11127, 11157, 11163, 11166, 11172, 11181, 11199, 11217, 11301, 11337, 11343, 11361

Offset

1,1

Links

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

Mathematica

cf70Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 70]; Select[Range[11400], cf70Q] (* Harvey P. Dale, May 31 2021 *)

Crossrefs

Sequence in context: A321146 A107545 A256363 * A083607 A168028 A031834

Adjacent sequences: A031565 A031566 A031567 * A031569 A031570 A031571

Keyword

nonn

Author

David W. Wilson

Status

approved