%I #53 Aug 30 2023 09:45:48

%S 2,2,5,43,1201,191,181,911,169553,117307,4021,10746341,1201,228511817,

%T 13564461457,6568801,47072139617,29078814248401,13841169553,

%U 4058036683,810221830361,309079,83960385389,3421093417510114543,33232924804801,79787519018560501

%N Largest prime factor of 7^n + 1.

%H <a href="/A227575/b227575.txt">Table of n, a(n) for n = 0..387</a>

%H S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>

%F a(n) = A006530(A034491(n)). - _Vincenzo Librandi_, Jul 12 2016

%e 7^12 + 1 = 2*73*193*409*1201, so a(12) = 1201.

%t Table[FactorInteger[7^n + 1][[-1, 1]], {n, 0, 30}] (* _Bruno Berselli_, Aug 23 2013 *)

%o (PARI) a(n) = f = factor(7^n + 1); f[#f~, 1]; \\ _Michel Marcus_, Aug 22 2013

%o (Magma) [Maximum(PrimeDivisors(7^n+1)): n in [0..30]]; // _Bruno Berselli_, Aug 23 2013

%Y Cf. A006530, A034491.

%Y Cf. A002587, A074249, A074476, A074478.

%K nonn

%O 0,1

%A _Michel Marcus_, Aug 22 2013

%E Terms to a(100) in b-file from _Vincenzo Librandi_, Jul 12 2016

%E a(101)-a(372) in b-file from _Amiram Eldar_, Feb 02 2020

%E a(373)-a(387) in b-file from _Max Alekseyev_, Apr 25 2022, Aug 30 2023