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A031567
Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 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
OFFSET
1,1
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
KEYWORD
nonn
STATUS
approved