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 A355461 #8 Jul 03 2022 09:10:43 %S A355461 5,13,21,29,53,173,237,293,437,453,1133,1253 %N A355461 Squarefree numbers d of the form r^2*m^2 + 4*r, where r and m are odd positive integers, such that Q(sqrt(d)) has class number 1. %C A355461 In 1801, Gauss conjectured that there exist infinitely many real quadratic fields with class number one and the conjecture is still unproved, but there are only 12 real quadratic fields of class number one which are of the form Q(sqrt(r^2*m^2 + 4*r)), where the parameters r and m are odd integers. Those 12 values of d := r^2*m^2 + 4*r belong to the present sequence. %H A355461 A. Biró and K. Lapkova <a href="http://dx.doi.org/10.4064/aa7957-12-2015">The class number one problem for the real quadratic fields Q(sqrt(a*n^2+4*a))</a>, Acta Arith., vol. 172(2), 2016, pp. 117-131. %H A355461 A. Hoque and S. Kotyada <a href="https://doi.org/10.1007/s00013-020-01520-w">Class number one problem for the real quadratic fields Q(sqrt(m^2+2*r))</a>, Archiv der Mathematik, vol. 116(1), 2021, pp. 33-36. %e A355461 a(2) = 13 since h(13) = h(1^2*3^2 + 4*1) = 1. %Y A355461 Cf. A050950, A053329, A308420. %K A355461 nonn,fini,full %O A355461 1,1 %A A355461 _Marco Ripà_, Jul 02 2022