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 A133676 #16 Sep 24 2022 12:30:51 %S A133676 39,55,56,63,68,80,128,136,144,155,156,171,184,196,203,208,219,220, %T A133676 224,252,256,259,260,264,275,276,291,292,308,320,323,328,336,355,360, %U A133676 363,384,387,388,400,456,468,475,504,507,528,544,552,564,568,576,580,592 %N A133676 Negative discriminants with form class group of exponent 4 (negated). %C A133676 The sequence is finite. It appears to have exactly 485 terms, the largest being 887040. %C A133676 The finiteness of the sequence was proved by Earnest and Estes. %C A133676 I found the 485 terms with PARI and didn't find any other up to 50000000. %H A133676 David Brink, <a href="/A133676/b133676.txt">Table of n, a(n) for n = 1..485</a> %H A133676 David Brink, <a href="http://www.youtube.com/watch?v=l_yRq0oqKx4">Five peculiar theorems on simultaneous representation of primes by quadratic forms (Video abstract)</a> %H A133676 David Brink, <a href="http://dx.doi.org/10.1016/j.jnt.2008.04.007">Five peculiar theorems on simultaneous representation of primes by quadratic forms</a>, J. Number Theory 129 (2009), no. 2, 464-468. %H A133676 A. G. Earnest and D. R. Estes, <a href="http://dx.doi.org/10.1112/S0025579300010214">An algebraic approach to the growth of class numbers of binary quadratic lattices</a>, Mathematika 28 (1981), no. 2, 160--168. %H A133676 Journal of Number Theory, <a href="http://www.youtube.com/user/JournalNumberTheory">Video Abstracts</a> %o A133676 (PARI) a(n) = if(n%4==0 || n%4==3, my(v = quadclassunit(-n)[2]); (#v > 0) && (v[1] == 4), 0) \\ _Jianing Song_, Sep 24 2022 %Y A133676 Cf. A003173, A317987 (subsequence). %K A133676 nonn,fini %O A133676 1,1 %A A133676 _David Brink_, Dec 29 2007