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 A176689 #9 Sep 06 2016 04:13:15 %S A176689 3,5,17,257,641,65537,274177,6700417,67280421310721 %N A176689 Prime factors of 2^128 - 1. %t A176689 First/@FactorInteger[2^128-1] %o A176689 (PARI) factor(2^128 - 1)[,1] \\ _Charles R Greathouse IV_, Sep 06 2016 %Y A176689 Cf. A000215, A002590, A019434, A023394, A050922, A070592. %K A176689 fini,full,nonn %O A176689 1,1 %A A176689 _Vladimir Joseph Stephan Orlovsky_, Apr 23 2010 %E A176689 Edited by _T. D. Noe_, May 06 2010 %E A176689 Typo in definition corrected by _Arkadiusz Wesolowski_, Feb 17 2011