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 A197172 #9 Aug 02 2019 21:08:37
%S A197172 69,87,93,159,177,183,249,267,276,312,321,327,348,372,387,417,471,597,
%T A197172 633,636,699,711,717,723,741,747,831,849,879,921,927,987,993,1005,
%U A197172 1068,1104,1137,1179,1248,1251,1272,1293,1299,1317,1320,1353,1359,1383,1392
%N A197172 Values k such that singular quadratic unity of Q(k) have gcd(k, y) = 3.
%t A197172 cr = {}; ck = {}; 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[ck, GCD[d4, n]]; AppendTo[cr, n]]], {n, 2, 200000}]; aa = {}; Do[If[ck[[n]] == 3, AppendTo[aa, cr[[n]]]], {n, 1, Length[cr]}]; aa
%Y A197172 Cf. A087643, A172000, A194366, A197115, A197127, A197128, A197170, A197171.
%K A197172 nonn
%O A197172 2,1
%A A197172 _Artur Jasinski_, Oct 11 2011