This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A074479 Largest prime factor of 5^n - 1. 6

%I

%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 Vincenzo Librandi, <a href="/A074479/b074479.txt">Table of n, a(n) for n = 1..100</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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.