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A031566 Numbers n such that continued fraction for sqrt(n) has even period and central term 68. 0
4626, 4642, 4678, 4694, 4702, 4722, 4726, 4742, 4766, 4786, 4798, 4802, 4806, 4818, 4822, 4834, 4838, 4846, 4854, 4866, 4882, 4894, 4898, 10407, 10446, 10452, 10473, 10479, 10497, 10524, 10533, 10551, 10569, 10581, 10587, 10596, 10617, 10623, 10641 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

cf68Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]]==68]; Select[Range[11000], cf68Q] (* Harvey P. Dale, Jan 10 2019 *)

CROSSREFS

Sequence in context: A115446 A254850 A139410 * A236815 A233855 A068268

Adjacent sequences:  A031563 A031564 A031565 * A031567 A031568 A031569

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified June 6 04:15 EDT 2020. Contains 334859 sequences. (Running on oeis4.)