A031589 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 91.

8283, 8287, 8291, 8311, 8331, 8351, 8363, 8371, 8387, 8403, 8419, 8423, 8431, 8443, 8447, 8459, 8467, 8483, 8519, 8523, 8527, 8531, 8539, 8543, 8551, 8563, 8599, 8623, 8627, 8647, 33128, 33160, 33184, 33256, 33280, 33408, 33416, 33448, 33472, 33504

Offset

1,1

Links

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

Mathematica

cf91Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s]][[2]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]]==91]; Select[Range[34000], cf91Q]//Quiet (* Harvey P. Dale, Feb 01 2019 *)

Crossrefs

Sequence in context: A203881 A145527 A054215 * A031769 A280872 A329342

Adjacent sequences: A031586 A031587 A031588 * A031590 A031591 A031592

Keyword

nonn

Author

David W. Wilson

Status

approved