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 A133288 #5 Jul 20 2018 17:42:07
%S A133288 15,20,24,32,35,36,40,48,51,52,60,64,72,75,84,88,91,96,99,100,112,115,
%T A133288 120,123,132,147,148,160,168,180,187,192,195,228,232,235,240,267,280,
%U A133288 288,312,315,340,352,372,403,408,420,427,435,448,480,483,520,532,555,595,627,660,672,708,715,760
%N A133288 Negative discriminants with form class group of exponent 2 (negated).
%D A133288 D. A. Cox, Primes of the form x^2+ny^2, Wiley, New York, 1989.
%D A133288 D. E. Flath, Introduction to Number Theory, Wiley-Interscience, 1989.
%H A133288 Andrew Howroyd, <a href="/A133288/b133288.txt">Table of n, a(n) for n = 1..88</a>
%o A133288 (PARI) ok(n)={(-n)%4<2 && quadclassunit(-n).no > 1 && !#select(k->k<>2, quadclassunit(-n).cyc)} \\ _Andrew Howroyd_, Jul 20 2018
%Y A133288 Cf. A003171 is the disjoint union of A133675 and this sequence.
%K A133288 fini,nonn
%O A133288 1,1
%A A133288 _David Brink_, Dec 30 2007