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 A031616 #16 Aug 18 2021 00:10:32
%S A031616 5209,16210,16465,16981,24457,35513,45169,46021,58853,59338,60314,
%T A031616 72185,74345,75437,92857,106154,107458,108113,110753,123826,124529,
%U A031616 125941,127361,128074,128789,131669,151273,168941,170585,172237,173897
%N A031616 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 28.
%t A031616 cf28Q[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]] == 28]; Rest[Select[Range[174000],cf28Q]] (* _Harvey P. Dale_, Jun 24 2020 *)
%Y A031616 Subsequence of A003814.
%K A031616 nonn
%O A031616 1,1
%A A031616 _David W. Wilson_
%E A031616 First term 785 removed by _Georg Fischer_, Jun 16 2019