A031603 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 15.

2858, 3074, 5122, 7177, 7517, 9773, 10169, 13681, 14149, 16673, 17189, 17713, 17978, 18514, 20525, 21097, 22265, 22861, 26041, 27337, 27997, 30113, 32213, 33653, 35594, 35969, 37489, 37874, 38261, 39041, 39434, 39829, 45673, 52825, 54785, 55717

Offset

1,1

Links

Table of n, a(n) for n=1..36.

Mathematica

opct15Q[n_]:=Module[{sr=Sqrt[n], cf, len}, cf=If[IntegerQ[sr], {}, ContinuedFraction[ sr][[2]]]; len=Length[cf]; OddQ[len]&&Take[cf, {Floor[ len/2], Floor[len/2]+1}]=={15, 15}]; Select[Range[56000], opct15Q] (* Harvey P. Dale, Jun 11 2013 *)

Crossrefs

Subsequence of A003814.

Sequence in context: A250637 A067703 A253714 * A236586 A233379 A192087

Adjacent sequences: A031600 A031601 A031602 * A031604 A031605 A031606

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected by Harvey P. Dale, Jun 11 2013

Status

approved