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 A033266 #11 Jun 10 2018 02:37:54
%S A033266 5,6,8,9,10,12,13,15,16,18,22,25,28,37,58
%N A033266 Numbers n such that every genus of binary quadratic forms of discriminant -4n consists of a single class and the class number h(-4n) = 2.
%D A033266 David A. Cox, "Primes of the Form x^2 + n y^2", Wiley, 1989, p. 60.
%D A033266 G. B. Mathews, Theory of Numbers, Chelsea, no date, p. 263.
%o A033266 (PARI) ok(n)={my(u=quadclassunit(-4*n).cyc); #u==1 && !select(t->t<>2, u)} \\ _Andrew Howroyd_, Jun 09 2018
%Y A033266 A subsequence of A000926.
%Y A033266 Cf. A033267, A033268, A033269.
%K A033266 nonn,fini,full
%O A033266 1,1
%A A033266 _N. J. A. Sloane_