A031567 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 69.

4763, 4779, 4783, 4787, 4799, 4803, 4811, 4827, 4831, 4859, 4871, 4879, 4883, 4903, 4919, 4923, 4931, 4943, 4947, 4951, 4967, 4987, 4991, 4999, 5003, 5011, 5023, 5027, 5039, 19048, 19072, 19104, 19112, 19200, 19296, 19328, 19456, 19488, 19496, 19520

Offset

1,1

Links

Table of n, a(n) for n=1..40.

Mathematica

cf69Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len= Length[ cf]; EvenQ[len]&&cf[[len/2]]==69]; Select[Range[20000], cf69Q] (* Harvey P. Dale, Jul 06 2019 *)

Crossrefs

Sequence in context: A258231 A257763 A260293 * A031747 A125949 A237214

Adjacent sequences: A031564 A031565 A031566 * A031568 A031569 A031570

Keyword

nonn

Author

David W. Wilson

Status

approved