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 A218038 #8 Feb 16 2025 08:33:18 %S A218038 235,346,427,506,574,697,785,786,842,874,894,895,898,899,906,985,1086, %T A218038 1191,1211,1339,1342,1345,1406,1527,1546,1639,1735,1758,1765,1851, %U A218038 1866,1882,1937,1954,2118,2230,2233,2263,2298,2495,2505,2510,2554,2666,2678,2726 %N A218038 Numbers n such that Q(sqrt(n)) has class number 6. %H A218038 Charles R Greathouse IV, <a href="/A218038/b218038.txt">Table of n, a(n) for n = 1..10000</a> %H A218038 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %t A218038 Select[Range[2726], SquareFreeQ[#] && NumberFieldClassNumber@Sqrt[#] == 6 &] %o A218038 (PARI) is(n)=issquarefree(n) && qfbclassno(if(n%4>1,4,1)*n)==6 \\ _Charles R Greathouse IV_, Jan 19 2017 %Y A218038 Cf. A003172, A029702-A029705, A218039-A218042. %K A218038 nonn %O A218038 1,1 %A A218038 _Arkadiusz Wesolowski_, Oct 19 2012