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%I #25 Sep 08 2022 08:45:07
%S 2,3,31,13,71,31,19531,313,829,521,12207031,601,305175781,19531,1741,
%T 11489,466344409,5167,3981071,9161,519499,12207031,332207361361,
%U 390001,9384251,305175781,31051,234750601,22125996444329,7621
%N Largest prime factor of 5^n - 1.
%H <a href="/A074479/b074479.txt">Table of n, a(n) for n = 1..502</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(A024049(n)). - _Vincenzo Librandi_, Jul 13 2016
%e 5^9 - 1 = 1953124 = (2^2)*19*31*829, so a(9) = 829.
%t Table[FactorInteger[5^n - 1] [[-1, 1]], {n, 30}] (* _Vincenzo Librandi_, Aug 23 2013 *)
%o (PARI) for(n=1,32, v=factor(5^n-1); print1(v[matsize(v)[1],1],","))
%o (Magma) [Maximum(PrimeDivisors(5^n-1)): n in [1..45]]; // _Vincenzo Librandi_, Jul 13 2016
%Y Cf. A074478 (largest prime factor of 5^n + 1), A074477 (largest prime factor of 3^n - 1), A074249 (largest prime factor of 7^n - 1).
%Y Cf. A006530, A024049.
%Y Cf. similar sequences listed in A274906.
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Aug 23 2002
%E Terms to a(100) in b-file from _Vincenzo Librandi_, Aug 23 2013
%E a(101)-a(448) in b-file from _Amiram Eldar_, Feb 01 2020
%E a(449)-a(502) in b-file from _Max Alekseyev_, Apr 25 2022
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