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 A218041 #8 Feb 16 2025 08:33:18 %S A218041 1129,1654,3137,3719,4409,4534,5521,5623,5878,6809,7573,7873,9998, %T A218041 10273,10721,10814,11027,11641,12323,12409,12657,13069,13691,14159, %U A218041 15374,15629,16321,16382,17273,17989,18633,19441,21023,21781,22497,22502,23003,23806 %N A218041 Numbers n such that Q(sqrt(n)) has class number 9. %H A218041 Charles R Greathouse IV, <a href="/A218041/b218041.txt">Table of n, a(n) for n = 1..10000</a> %H A218041 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %t A218041 Select[Range[23806], SquareFreeQ[#] && NumberFieldClassNumber@Sqrt[#] == 9 &] %o A218041 (PARI) is(n)=issquarefree(n) && qfbclassno(if(n%4>1,4,1)*n)==9 \\ _Charles R Greathouse IV_, Jan 19 2017 %Y A218041 Cf. A003172, A029702-A029705, A218038-A218040, A218042. %K A218041 nonn %O A218041 1,1 %A A218041 _Arkadiusz Wesolowski_, Oct 19 2012