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 A020406 #19 Aug 24 2025 04:14:20
%S A020406 1381,1789,2521,3754,3994,5953,6389,7349,7765,7801,8297,8842,9274,
%T A020406 10253,12413,14458,15349,15749,16073,16229,19073,21485,22433,24106,
%U A020406 24317,24506,24538,24929,25577,25706,26170,26773,26954,28018,28345,30197,32218,32290
%N A020406 Numbers k such that the continued fraction for sqrt(k) has period 67.
%H A020406 Amiram Eldar, <a href="/A020406/b020406.txt">Table of n, a(n) for n = 1..10000</a>
%t A020406 cf67Q[n_]:=Module[{s=Sqrt[n]},If[IntegerQ[s],1,Length[ ContinuedFraction[ s][[2]]]]==67]; Select[Range[33000],cf67Q] (* _Harvey P. Dale_, Sep 21 2018 *)
%Y A020406 Cf. A003285.
%K A020406 nonn,changed
%O A020406 1,1
%A A020406 _David W. Wilson_