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 A074476 #28 Jul 25 2023 19:33:57
%S A074476 2,2,5,7,41,61,73,547,193,37,1181,661,6481,398581,16493,271,21523361,
%T A074476 1021,530713,101917,42521761,2269,570461,23535794707,769,22996651,
%U A074476 4795973261,19927,647753,5385997,47763361,22434744889,926510094425921
%N A074476 Largest prime factor of 3^n + 1.
%H A074476 <a href="/A074476/b074476.txt">Table of n, a(n) for n = 0..691</a>
%H A074476 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%F A074476 a(n) = A006530(A034472(n)). - _Amiram Eldar_, Feb 01 2020
%t A074476 Table[FactorInteger[3^n + 1][[-1, 1]], {n, 0, 40}] (* _Vincenzo Librandi_, Aug 23 2013 *)
%o A074476 (PARI) for(n=0,35, v=factor(3^n+1); print1(v[matsize(v)[1],1],","))
%o A074476 (Magma) [Maximum(PrimeDivisors(3^n+1)): n in [0..40]]; // _Vincenzo Librandi_, Aug 23 2013
%Y A074476 Cf. A006530, A034472, A074477 (largest prime factor of 3^n - 1), A002587 (largest prime factor of 2^n + 1), A074478 (largest prime factor of 5^n + 1).
%K A074476 nonn
%O A074476 0,1
%A A074476 _Rick L. Shepherd_, Aug 23 2002
%E A074476 Terms to a(100) in b-file from _Vincenzo Librandi_, Aug 23 2013
%E A074476 a(101)-a(658) in b-file from _Amiram Eldar_, Feb 01 2020
%E A074476 a(659)-a(691) in b-file from _Max Alekseyev_, Apr 25 2022, Jul 25 2023