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A074479
Largest prime factor of 5^n - 1.
13
2, 3, 31, 13, 71, 31, 19531, 313, 829, 521, 12207031, 601, 305175781, 19531, 1741, 11489, 466344409, 5167, 3981071, 9161, 519499, 12207031, 332207361361, 390001, 9384251, 305175781, 31051, 234750601, 22125996444329, 7621
OFFSET
1,1
FORMULA
a(n) = A006530(A024049(n)). - Vincenzo Librandi, Jul 13 2016
EXAMPLE
5^9 - 1 = 1953124 = (2^2)*19*31*829, so a(9) = 829.
MATHEMATICA
Table[FactorInteger[5^n - 1] [[-1, 1]], {n, 30}] (* Vincenzo Librandi, Aug 23 2013 *)
PROG
(PARI) for(n=1, 32, v=factor(5^n-1); print1(v[matsize(v)[1], 1], ", "))
(Magma) [Maximum(PrimeDivisors(5^n-1)): n in [1..45]]; // Vincenzo Librandi, Jul 13 2016
CROSSREFS
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).
Cf. similar sequences listed in A274906.
Sequence in context: A114009 A307453 A143665 * A272043 A136150 A155056
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Aug 23 2002
EXTENSIONS
Terms to a(100) in b-file from Vincenzo Librandi, Aug 23 2013
a(101)-a(448) in b-file from Amiram Eldar, Feb 01 2020
a(449)-a(502) in b-file from Max Alekseyev, Apr 25 2022
STATUS
approved