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 A145688 #8 Jun 30 2015 13:18:43 %S A145688 3,19,11,17,73,43,163,67,113,131,41,193,59,241,89,883,353,1153,139, %T A145688 1459,523,1801,641,683,2179,257,2593,83,107,179,97,3529,137,1291,4051, %U A145688 491,419,1601,1667,601,1873,307,2017,2243,211,379,827,233,467,2731,313,8713 %N A145688 Primitive prime factors of the sequence 2k^2 + 1 in the order that they are found. %C A145688 a(n) mod 8 = 1 or 3. %H A145688 Bernhard Helmes, <a href="http://www.devalco.de/quadr_Sieb_2x%5E2+1.php">Prime sieving on the polynomial f(n)=2n^2+1</a>. %Y A145688 Cf. A144851. %K A145688 nonn %O A145688 1,1 %A A145688 Bernhard Helmes (pi(AT)devalco.de), Oct 16 2008