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 A218039 #8 Feb 16 2025 08:33:18 %S A218039 577,1009,1087,1294,1601,1761,1934,2029,2251,2302,2467,2913,4139,4229, %T A218039 4702,5039,5273,5417,5743,5827,6151,6598,7919,8097,8311,8462,8661, %U A218039 8773,9029,9049,9101,9289,9326,9539,10117,10313,10357,10713,10957,11021,11053,11269 %N A218039 Numbers n such that Q(sqrt(n)) has class number 7. %H A218039 Charles R Greathouse IV, <a href="/A218039/b218039.txt">Table of n, a(n) for n = 1..10000</a> %H A218039 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %t A218039 Select[Range[11269], SquareFreeQ[#] && NumberFieldClassNumber@Sqrt[#] == 7 &] %o A218039 (PARI) is(n)=issquarefree(n) && qfbclassno(if(n%4>1,4,1)*n)==7 \\ _Charles R Greathouse IV_, Jan 19 2017 %Y A218039 Cf. A003172, A029702-A029705, A218038, A218040-A218042. %K A218039 nonn %O A218039 1,1 %A A218039 _Arkadiusz Wesolowski_, Oct 19 2012