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 A031399 #9 Aug 30 2014 18:57:19 %S A031399 4,8,16,20,25,32,34,40,52,64,68,80,100,104,116,128,136,146,148,160, %T A031399 164,169,178,194,200,205,208,212,221,232,244,256,260,272,289,292,296, %U A031399 305,320,328,340,356,377,386,388,400,404,410,416,424,436,452 %N A031399 Numbers n with no 4k+3 factors such that Pell equation x^2 - n y^2 = -1 insoluble. %D A031399 "Advanced Number Theory" by Harvey Cohn. %H A031399 Joerg Arndt, <a href="http://www.jjj.de/fxt/#fxtbook">Matters Computational (The Fxtbook)</a> %Y A031399 Cf. A031396, A031397, A031398. %K A031399 nonn %O A031399 1,1 %A A031399 _David W. Wilson_