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 A031615 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 27. 0
 4649, 9458, 15457, 15706, 22621, 31853, 32569, 41434, 53189, 54113, 56458, 66925, 67961, 81097, 82237, 99754, 101653, 102929, 114869, 115546, 116906, 118274, 121034, 121729, 122426, 137629, 154505, 160841, 162445, 164057, 175685, 176522, 178202, 179890 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..34. MATHEMATICA cf27Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {0, 0}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len] && cf[[(len+1)/2]]==27]; Select[Range[200000], cf27Q] (* Harvey P. Dale, Mar 27 2015 *) CROSSREFS Sequence in context: A068268 A227482 A028551 * A122713 A235235 A118815 Adjacent sequences: A031612 A031613 A031614 * A031616 A031617 A031618 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS Corrected and extended by Harvey P. Dale, Mar 27 2015 STATUS approved

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Last modified February 24 11:15 EST 2024. Contains 370303 sequences. (Running on oeis4.)