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 A144861 #9 Jun 30 2015 10:04:47 %S A144861 7,17,31,71,97,127,23,199,241,41,337,449,73,577,647,103,47,881,967, %T A144861 151,1151,1249,193,1567,257,113,89,311,2311,79,2591,2887,3041,457, %U A144861 3361,3527,3697,4049,4231,631,271,4801,4999,743,5407,137,263,6271,6961,313,1063 %N A144861 Primitive prime factors of the sequence 2k^2 - 1 in the order in which they are first found. %C A144861 Every Mersenne prime number appears on this sequence. a(n) mod 8 = 1 or 7. %H A144861 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>. %t A144861 Rest[DeleteDuplicates[#[[1]]&/@(Flatten[FactorInteger/@(2*Range[100]^2-1),1])]] (* _Harvey P. Dale_, Nov 15 2014 *) %Y A144861 Cf. A005529, A144848. %K A144861 nonn %O A144861 2,1 %A A144861 Bernhard Helmes (pi(AT)devalco.de), Sep 23 2008 %E A144861 Definition clarified by _Harvey P. Dale_, Nov 15 2014