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 A031599 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 11. 1
 809, 2581, 2785, 2890, 4217, 5353, 6949, 7114, 7621, 9698, 9893, 10289, 11177, 11597, 12461, 15325, 15817, 17429, 18218, 18754, 19298, 19946, 20506, 20789, 21361, 22234, 23833, 25693, 27085, 27737, 29065, 29741, 30202, 30425, 30545, 30890, 31237, 32290 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..38. MATHEMATICA cf11Q[n_]:=Module[{s=Sqrt[n], len, cf}, cf=If[IntegerQ[s], {2, 2}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 11]; Select[Range[32000], cf11Q] (* Harvey P. Dale, Mar 18 2018 *) CROSSREFS Sequence in context: A160034 A273811 A252028 * A265984 A332848 A160561 Adjacent sequences: A031596 A031597 A031598 * A031600 A031601 A031602 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS Corrected and extended by Harvey P. Dale, Mar 18 2018 Definitions of A031599-A031688 clarified by N. J. A. Sloane, Aug 17 2021 STATUS approved

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Last modified August 13 14:10 EDT 2024. Contains 375142 sequences. (Running on oeis4.)