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 A031616 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 28. 0
 5209, 16210, 16465, 16981, 24457, 35513, 45169, 46021, 58853, 59338, 60314, 72185, 74345, 75437, 92857, 106154, 107458, 108113, 110753, 123826, 124529, 125941, 127361, 128074, 128789, 131669, 151273, 168941, 170585, 172237, 173897 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..31. MATHEMATICA cf28Q[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]] == 28]; Rest[Select[Range[174000], cf28Q]] (* Harvey P. Dale, Jun 24 2020 *) CROSSREFS Subsequence of A003814. Sequence in context: A109159 A231113 A289514 * A067224 A204139 A237408 Adjacent sequences: A031613 A031614 A031615 * A031617 A031618 A031619 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS First term 785 removed by Georg Fischer, Jun 16 2019 STATUS approved

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Last modified February 25 00:32 EST 2024. Contains 370308 sequences. (Running on oeis4.)