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 A031567 Numbers n such that continued fraction for sqrt(n) has even period and central term 69. 0
 4763, 4779, 4783, 4787, 4799, 4803, 4811, 4827, 4831, 4859, 4871, 4879, 4883, 4903, 4919, 4923, 4931, 4943, 4947, 4951, 4967, 4987, 4991, 4999, 5003, 5011, 5023, 5027, 5039, 19048, 19072, 19104, 19112, 19200, 19296, 19328, 19456, 19488, 19496, 19520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MATHEMATICA cf69Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]]==69]; Select[Range[20000], cf69Q] (* Harvey P. Dale, Jul 06 2019 *) CROSSREFS Sequence in context: A258231 A257763 A260293 * A031747 A125949 A237214 Adjacent sequences:  A031564 A031565 A031566 * A031568 A031569 A031570 KEYWORD nonn AUTHOR STATUS approved

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Last modified May 7 20:36 EDT 2021. Contains 343652 sequences. (Running on oeis4.)