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A031563
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 65.
0
4227, 4231, 4243, 4247, 4259, 4271, 4283, 4299, 4307, 4319, 4327, 4339, 4363, 4391, 4411, 4419, 4423, 4443, 4447, 4451, 4463, 4467, 4483, 4487, 16904, 16928, 16936, 16992, 17000, 17024, 17056, 17088, 17096, 17120, 17128, 17152, 17216, 17224, 17248
OFFSET
1,1
MATHEMATICA
cf65Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 65]; Select[Range[17300], cf65Q] (* Harvey P. Dale, Dec 29 2019 *)
CROSSREFS
Sequence in context: A097226 A202488 A167037 * A031743 A236725 A345580
KEYWORD
nonn
STATUS
approved