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A074478 Largest prime factor of 5^n + 1. 5
2, 3, 13, 7, 313, 521, 601, 449, 11489, 5167, 9161, 5281, 390001, 38923, 234750601, 7621, 29423041, 41540861, 6597973, 213029, 632133361, 7603, 1030330938209, 42272797713043, 152587500001, 50150933101, 83181652304609, 16018507 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..100

S. S. Wagstaff, Jr., The Cunningham Project

FORMULA

a(n) = A006530(A034474(n)). - Michel Marcus, Jul 09 2016

EXAMPLE

5^11 + 1 = 48828126 = 2*3*23*67*5281, so a(11) = 5281.

MATHEMATICA

Table[FactorInteger[5^n + 1][[-1, 1]], {n, 0, 30}] (* Bruno Berselli, Aug 23 2013 *)

PROG

(PARI) for(n=0, 30, v=factor(5^n+1); print1(v[matsize(v)[1], 1], ", "))

(MAGMA) [Maximum(PrimeDivisors(5^n+1)): n in [0..30]]; // Vincenzo Librandi, Jul 09 2016

CROSSREFS

Cf. A002587 (largest prime factor of 2^n + 1), A074479 (largest prime factor of 5^n - 1), A074476 (largest prime factor of 3^n + 1), A227575 (largest prime factor of 7^n + 1).

Cf. A006530, A034474.

Sequence in context: A192362 A057776 A110362 * A046421 A132365 A129671

Adjacent sequences:  A074475 A074476 A074477 * A074479 A074480 A074481

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Aug 23 2002

STATUS

approved

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Last modified September 20 12:42 EDT 2018. Contains 315239 sequences. (Running on oeis4.)