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A031619 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 31. 0
6109, 12149, 19681, 20530, 30397, 40973, 55921, 57346, 70514, 71578, 73189, 87977, 89165, 91565, 110665, 111997, 128693, 132298, 133754, 151169, 151946, 155861, 157441, 159029, 159826, 178813, 203341, 206957, 212441, 234250, 235217, 236186, 237157, 238130 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
cf31Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 31]; Select[Range[250000], cf31Q] (* Harvey P. Dale, Jun 01 2018 *)
CROSSREFS
Sequence in context: A211929 A251994 A201225 * A235764 A235547 A345186
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected and extended by Harvey P. Dale, Jun 01 2018
STATUS
approved

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Last modified April 22 01:34 EDT 2024. Contains 371887 sequences. (Running on oeis4.)