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A031608 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 20. 0
2729, 5233, 8362, 8917, 24874, 29873, 31973, 37997, 38777, 46237, 54818, 56698, 57173, 58129, 64129, 64634, 65141, 66161, 66674, 67189, 67706, 68746, 74713, 87277, 88457, 89645, 90841, 100186, 101450, 104002, 104645, 115333, 116689, 126541 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
cf20Q[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]]] ==20]; Select[ Range[ 130000], cf20Q] (* Harvey P. Dale, Sep 18 2021 *)
CROSSREFS
Subsequence of A003814.
Sequence in context: A290644 A231289 A212725 * A350047 A043579 A166780
KEYWORD
nonn
AUTHOR
EXTENSIONS
First term 401 removed by Georg Fischer, Jun 16 2019
STATUS
approved

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Last modified May 26 09:40 EDT 2024. Contains 372824 sequences. (Running on oeis4.)