This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A031666 #16 Dec 16 2023 11:22:01
%S A031666 13933,123985,124690,126106,185021,258233,260269,262313,347146,550925,
%T A031666 553897,559865,679417,823178,953201,957109,959066,962986,964949,
%U A031666 966914,972821,974794,1120093,1286797,1295885,1467482,1474757,1477186
%N A031666 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 78.
%t A031666 cf78Q[n_]:=Module[{s=Sqrt[n],len,cf},cf=If[IntegerQ[s],{1,1},ContinuedFraction[s][[2]]];len= Length[ cf];OddQ[len]&&cf[[Floor[len/2]]]==cf[[Ceiling[len/2]]]==78]; Select[Range[ 1480000],cf78Q] (* _Harvey P. Dale_, Dec 16 2023 *)
%Y A031666 Subsequence of A003814.
%K A031666 nonn
%O A031666 1,1
%A A031666 _David W. Wilson_
%E A031666 First term 6085 removed by _Georg Fischer_, Jun 16 2019