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 A031603 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 15. 0
 2858, 3074, 5122, 7177, 7517, 9773, 10169, 13681, 14149, 16673, 17189, 17713, 17978, 18514, 20525, 21097, 22265, 22861, 26041, 27337, 27997, 30113, 32213, 33653, 35594, 35969, 37489, 37874, 38261, 39041, 39434, 39829, 45673, 52825, 54785, 55717 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..36. MATHEMATICA opct15Q[n_]:=Module[{sr=Sqrt[n], cf, len}, cf=If[IntegerQ[sr], {}, ContinuedFraction[ sr][[2]]]; len=Length[cf]; OddQ[len]&&Take[cf, {Floor[ len/2], Floor[len/2]+1}]=={15, 15}]; Select[Range[56000], opct15Q] (* Harvey P. Dale, Jun 11 2013 *) CROSSREFS Subsequence of A003814. Sequence in context: A250637 A067703 A253714 * A236586 A233379 A192087 Adjacent sequences: A031600 A031601 A031602 * A031604 A031605 A031606 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS Corrected by Harvey P. Dale, Jun 11 2013 STATUS approved

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Last modified June 15 02:53 EDT 2024. Contains 373402 sequences. (Running on oeis4.)