A020360 Numbers k such that the continued fraction for sqrt(k) has period 21.

181, 277, 394, 397, 409, 433, 641, 809, 953, 1217, 1277, 1489, 1637, 1861, 2089, 2146, 2257, 2314, 2393, 2425, 2693, 2762, 2825, 3098, 3425, 3977, 3989, 4777, 5165, 5237, 5669, 5785, 6122, 6610, 7045, 7306, 7673, 7717, 7738, 7946, 8146, 8938, 9010, 9250

Offset

1,1

Links

Table of n, a(n) for n=1..44.

Mathematica

cf21Q[n_]:=Module[{s=Sqrt[n]}, If[IntegerQ[s], 1, Length[ ContinuedFraction[ s][[2]]]]==21]; Select[Range[10000], cf21Q] (* Harvey P. Dale, Sep 22 2019 *)

Crossrefs

Sequence in context: A330366 A107694 A142312 * A238670 A168473 A142920

Adjacent sequences: A020357 A020358 A020359 * A020361 A020362 A020363

Keyword

nonn

Author

David W. Wilson

Status

approved