A031584 - OEIS

%I #14 Jul 06 2024 16:12:15

%S 7398,7414,7438,7446,7454,7458,7478,7506,7534,7542,7554,7558,7586,

%T 7606,7634,7646,7654,7666,7682,7694,7698,7702,7718,7726,7734,7742,

%U 16644,16653,16671,16689,16743,16773,16782,16788,16809,16833,16869,16917,16941,16953

%N 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 86.

%t cf86Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{1}, ContinuedFraction[ s][[2]]];len=Length[cf];EvenQ[len]&&cf[[len/2]] == 86]; Select[ Range[17000],cf86Q] (* _Harvey P. Dale_, Jan 15 2019 *)

%K nonn

%O 1,1

%A _David W. Wilson_