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A031586 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 88. 0

%I #12 Aug 17 2021 23:48:27

%S 7746,7778,7782,7814,7822,7838,7842,7846,7862,7874,7886,7894,7906,

%T 7934,7954,7974,7986,8002,8006,8014,8018,8038,8054,8078,8098,17427,

%U 17463,17481,17499,17502,17508,17517,17529,17553,17601,17607,17637,17652,17709

%N 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 88.

%t cf88Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{1}, ContinuedFraction[ s][[2]]];len=Length[cf];EvenQ[len]&&cf[[len/2]] == 88]; Select[ Range[18000],cf88Q] (* _Harvey P. Dale_, Sep 13 2018 *)

%K nonn

%O 1,1

%A _David W. Wilson_

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Last modified September 23 14:27 EDT 2023. Contains 365551 sequences. (Running on oeis4.)