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A031515 that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 17. 0
291, 307, 311, 331, 339, 343, 347, 359, 1160, 1184, 1192, 1216, 1248, 1256, 1280, 1312, 1344, 1352, 1376, 1384, 1408, 1440, 2607, 2823, 2895, 2955, 3039, 3183, 3243, 4632, 4696, 4744, 4824, 4952, 5016, 5128, 5144, 5272, 5384, 5464, 5528, 5592, 5768, 7235 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

okQ[k_] := Module[{c, lc}, If[IntegerQ[Sqrt[k]], False,

     c = ContinuedFraction[Sqrt[k]]; lc = Length[c[[2]]];

     EvenQ[lc] && c[[2, lc/2]] == 17]];

Select[Range[10000], okQ] (* Jean-Fran├žois Alcover, Jul 09 2021 *)

CROSSREFS

Sequence in context: A186548 A091740 A098250 * A090890 A123913 A031695

Adjacent sequences:  A031512 A031513 A031514 * A031516 A031517 A031518

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified January 22 23:50 EST 2022. Contains 350504 sequences. (Running on oeis4.)