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 A227575 #53 Aug 30 2023 09:45:48
%S A227575 2,2,5,43,1201,191,181,911,169553,117307,4021,10746341,1201,228511817,
%T A227575 13564461457,6568801,47072139617,29078814248401,13841169553,
%U A227575 4058036683,810221830361,309079,83960385389,3421093417510114543,33232924804801,79787519018560501
%N A227575 Largest prime factor of 7^n + 1.
%H A227575 <a href="/A227575/b227575.txt">Table of n, a(n) for n = 0..387</a>
%H A227575 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%F A227575 a(n) = A006530(A034491(n)). - _Vincenzo Librandi_, Jul 12 2016
%e A227575 7^12 + 1 = 2*73*193*409*1201, so a(12) = 1201.
%t A227575 Table[FactorInteger[7^n + 1][[-1, 1]], {n, 0, 30}] (* _Bruno Berselli_, Aug 23 2013 *)
%o A227575 (PARI) a(n) = f = factor(7^n + 1); f[#f~, 1]; \\ _Michel Marcus_, Aug 22 2013
%o A227575 (Magma) [Maximum(PrimeDivisors(7^n+1)): n in [0..30]]; // _Bruno Berselli_, Aug 23 2013
%Y A227575 Cf. A006530, A034491.
%Y A227575 Cf. A002587, A074249, A074476, A074478.
%K A227575 nonn
%O A227575 0,1
%A A227575 _Michel Marcus_, Aug 22 2013
%E A227575 Terms to a(100) in b-file from _Vincenzo Librandi_, Jul 12 2016
%E A227575 a(101)-a(372) in b-file from _Amiram Eldar_, Feb 02 2020
%E A227575 a(373)-a(387) in b-file from _Max Alekseyev_, Apr 25 2022, Aug 30 2023