A031654 - OEIS

%I #14 Aug 18 2021 00:10:32

%S 1090,10009,27581,89482,90682,134077,135545,185069,186793,246241,

%T 316133,321778,487645,581173,582698,585754,590353,593429,682901,

%U 686209,687866,691186,696181,699521,796393,814333,930137,937865,941741,1049537,1061861

%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 66.

%t op66Q[n_]:=Module[{s=Sqrt[n],cf,len},cf=If[IntegerQ[s],{1,1}, ContinuedFraction[ s][[2]]];len=Length[cf];OddQ[len]&&cf[[(len+1)/2]] == 66]; Select[Range[11*10^5],op66Q] (* _Harvey P. Dale_, Mar 14 2016 *)

%K nonn

%O 1,1

%A _David W. Wilson_

%E Terms corrected and definition corrected by _Harvey P. Dale_, Mar 14 2016