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 A020381 Numbers k such that the continued fraction for sqrt(k) has period 42. 0
 571, 724, 889, 907, 1081, 1348, 1477, 1576, 1619, 1633, 1636, 1732, 1786, 1841, 2073, 2167, 2253, 2276, 2339, 2344, 2433, 2493, 2518, 2611, 2819, 2821, 2896, 2901, 2939, 3039, 3070, 3142, 3154, 3203, 3284, 3430, 3439, 3467, 3513, 3523, 3546, 3556, 3573 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MATHEMATICA cf42Q[n_]:=Module[{s=Sqrt[n]}, If[IntegerQ[s], 1, Length[ ContinuedFraction[ s][[2]]]]==42]; Select[Range[4000], cf42Q] (* Harvey P. Dale, Sep 24 2019 *) CROSSREFS Sequence in context: A268248 A246229 A073036 * A142767 A251384 A076465 Adjacent sequences:  A020378 A020379 A020380 * A020382 A020383 A020384 KEYWORD nonn AUTHOR STATUS approved

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Last modified December 7 12:17 EST 2021. Contains 349581 sequences. (Running on oeis4.)