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A274908 Largest prime factor of 8^n - 1. 2
7, 7, 73, 13, 151, 73, 337, 241, 262657, 331, 599479, 109, 121369, 5419, 23311, 673, 131071, 262657, 1212847, 1321, 649657, 599479, 10052678938039, 38737, 10567201, 22366891, 97685839, 14449, 9857737155463, 18837001, 658812288653553079, 22253377 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..100

J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.

FORMULA

a(n) = A006530(A024088(n)). - Michel Marcus, Jul 11 2016

a(n) = A005420(3*n). - Robert Israel, Jul 12 2016

EXAMPLE

8^5 -1 = 32767 = 7*31*151, so a(5) = 151.

MAPLE

f:= n -> max(map(t -> max(numtheory:-factorset(subs(x=2, t[1]))), factors(x^(3*n)-1)[2])):

map(f, [$1..120]); # Robert Israel, Jul 12 2016

MATHEMATICA

Table[FactorInteger[8^n - 1][[-1, 1]], {n, 40}]

PROG

(MAGMA) [Maximum(PrimeDivisors(8^n-1)): n in [1..40]];

CROSSREFS

Cf. A005420, A006530, A024088.

Cf. similar sequences listed in A274906.

Sequence in context: A220079 A153272 A117860 * A009201 A219353 A269902

Adjacent sequences:  A274905 A274906 A274907 * A274909 A274910 A274911

KEYWORD

nonn

AUTHOR

Vincenzo Librandi, Jul 11 2016

STATUS

approved

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Last modified January 24 07:15 EST 2020. Contains 331189 sequences. (Running on oeis4.)