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 A031668 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 80. 0

%I #16 Jul 24 2022 15:48:47

%S 40829,132577,195485,197257,362629,365041,466778,473633,584057,587117,

%T 590185,850613,852458,1002626,1006634,1014674,1016689,1018706,1024769,

%U 1184473,1188829,1351085,1360397,1365065,1374425,1541042,1548497

%N 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 80.

%t cf80Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{0,0},ContinuedFraction[s][[2]]];len=Length[cf];OddQ[len]&&cf[[Floor[len/2]]]==cf[[Ceiling[len/2]]]==80]; Select[Range[155*10^4],cf80Q] (* _Harvey P. Dale_, Jul 24 2022 *)

%Y Subsequence of A003814.

%K nonn

%O 1,1

%A _David W. Wilson_

%E First term 6401 removed by _Georg Fischer_, Jun 16 2019

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Last modified July 19 20:58 EDT 2024. Contains 374436 sequences. (Running on oeis4.)