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 A218040 #8 Feb 16 2025 08:33:18 %S A218040 226,399,442,646,799,870,910,994,1023,1122,1155,1239,1290,1299,1351, %T A218040 1443,1446,1590,1705,1743,1785,1914,1947,1995,2010,2019,2035,2134, %U A218040 2210,2211,2310,2379,2402,2410,2415,2434,2451,2482,2490,2605,2705,2706,2730,2739,2751 %N A218040 Numbers n such that Q(sqrt(n)) has class number 8. %H A218040 Charles R Greathouse IV, <a href="/A218040/b218040.txt">Table of n, a(n) for n = 1..10000</a> %H A218040 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %t A218040 Select[Range[2751], SquareFreeQ[#] && NumberFieldClassNumber@Sqrt[#] == 8 &] %o A218040 (PARI) is(n)=issquarefree(n) && qfbclassno(if(n%4>1,4,1)*n)==8 \\ _Charles R Greathouse IV_, Jan 19 2017 %Y A218040 Cf. A003172, A029702-A029705, A218038-A218039, A218041-A218042. %K A218040 nonn %O A218040 1,1 %A A218040 _Arkadiusz Wesolowski_, Oct 19 2012