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 A031623 #16 Aug 18 2021 00:10:32
%S A031623 15178,25681,38537,52153,53069,53993,70981,72586,90289,91493,115961,
%T A031623 137341,140317,164554,166993,168629,170273,171098,192469,193346,
%U A031623 195989,196874,197761,201329,229213,258905,260941,262985,265037,267097,271241
%N A031623 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 35.
%t A031623 ct35Q[n_]:=Module[{s=Sqrt[n],cf,len,ctr},If[IntegerQ[s],cf={1,1},cf= ContinuedFraction[ s][[2]]];len=Length[cf];ctr=Floor[len/2];OddQ[len] && Take[cf,{ctr,ctr+1}]=={35,35}]; Select[Range[280000],ct35Q] (* _Harvey P. Dale_, Apr 16 2013 *)
%Y A031623 Subsequence of A003814.
%K A031623 nonn
%O A031623 1,1
%A A031623 _David W. Wilson_
%E A031623 Corrected by _Harvey P. Dale_, Apr 16 2013