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 A197128 #16 Mar 02 2017 13:12:27
%S A197128 2,3,5,7,8,10,11,12,13,15,17,18,19,20,21,23,24,26,27,28,29,31,32,33,
%T A197128 35,37,39,40,41,43,44,45,47,48,50,51,52,53,55,57,58,59,60,61,63,65,67,
%U A197128 68,71,72,73,74,75,76,77,79,80,82,83,84,85,88,89,90,91,92
%N A197128 Nonsquare positive integers n such that the fundamental unit of quadratic field Q(sqrt(n))is not singular.
%C A197128 x^2+n*y^2=(+/-)2^s where s is 0 or 1.
%C A197128 Definition: Unity is singular when GCD[n,y]<>1.
%t A197128 cr = {}; Do[If[IntegerQ[Sqrt[n]], , kk = NumberFieldFundamentalUnits[Sqrt[n]]; d1 = kk[[1]][[2]][[1]]; d2 = kk[[1]][[1]] kk[[1]][[2]][[2]]; d4 = Numerator[d2/Sqrt[n]]; If[GCD[d4, n] == 1, AppendTo[cr, n]]], {n, 2, 330}]; cr
%Y A197128 Cf. A087643, A172000, A194366, A197115, A197127.
%K A197128 nonn
%O A197128 1,1
%A A197128 _Artur Jasinski_, Oct 10 2011