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 A031603 #14 Aug 18 2021 00:10:32
%S A031603 2858,3074,5122,7177,7517,9773,10169,13681,14149,16673,17189,17713,
%T A031603 17978,18514,20525,21097,22265,22861,26041,27337,27997,30113,32213,
%U A031603 33653,35594,35969,37489,37874,38261,39041,39434,39829,45673,52825,54785,55717
%N A031603 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 15.
%t A031603 opct15Q[n_]:=Module[{sr=Sqrt[n],cf,len},cf=If[IntegerQ[sr],{}, ContinuedFraction[ sr][[2]]];len=Length[cf];OddQ[len]&&Take[cf,{Floor[ len/2],Floor[len/2]+1}]=={15,15}]; Select[Range[56000],opct15Q] (* _Harvey P. Dale_, Jun 11 2013 *)
%Y A031603 Subsequence of A003814.
%K A031603 nonn
%O A031603 1,1
%A A031603 _David W. Wilson_
%E A031603 Corrected by _Harvey P. Dale_, Jun 11 2013