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A031687 Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 99. 0
198997, 200785, 201682, 298237, 420073, 556741, 561226, 710938, 719393, 891497, 895277, 899065, 1086205, 1094557, 1098745, 1300129, 1311554, 1316138, 1533269, 1543189, 1545674, 1548161, 1553141, 1558129, 1560626, 1817833, 2062937 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
ct99Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len] && cf[[Floor[ len/2]]] == cf[[Ceiling[len/2]]]==99]; Select[Range[2063000], ct99Q] (* Harvey P. Dale, Oct 09 2021 *)
CROSSREFS
Sequence in context: A290780 A255782 A205638 * A234034 A154531 A043592
KEYWORD
nonn
AUTHOR
EXTENSIONS
First term 9802 removed by Georg Fischer, Jun 16 2019
STATUS
approved

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Last modified April 23 12:27 EDT 2024. Contains 371912 sequences. (Running on oeis4.)