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A031781 Period of continued fraction for sqrt(n) contains exactly 13 ones. 1
1219, 1591, 2071, 2107, 3375, 3655, 4175, 4399, 4671, 4847, 4888, 4891, 5319, 5395, 6208, 7067, 7144, 7515, 11800, 12328, 12875, 12947, 13144, 13199, 13511, 14027, 14319, 15151, 15272, 16120, 16403, 17331, 17759, 17936, 18483, 19327, 19527, 19691 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..650

MATHEMATICA

cf13Q[n_]:=Module[{s=Sqrt[n]}, If[IntegerQ[s], 1, Count[ ContinuedFraction[ s][[2]], 1]]==13]; Select[Range[20000], cf13Q] (* Harvey P. Dale, Jun 16 2017 *)

CROSSREFS

Sequence in context: A300408 A252600 A293479 * A069400 A233660 A015279

Adjacent sequences:  A031778 A031779 A031780 * A031782 A031783 A031784

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified September 16 17:38 EDT 2021. Contains 347473 sequences. (Running on oeis4.)