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A020360 Numbers n such that continued fraction for sqrt(n) has period 21. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 22 04:27 EST 2020. Contains 331133 sequences. (Running on oeis4.)