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A274908
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Largest prime factor of 8^n - 1.
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7
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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
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OFFSET
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1,1
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LINKS
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J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
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FORMULA
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EXAMPLE
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8^5 -1 = 32767 = 7*31*151, so a(5) = 151.
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MAPLE
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f:= n -> max(map(t -> max(numtheory:-factorset(subs(x=2, t[1]))), factors(x^(3*n)-1)[2])):
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MATHEMATICA
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Table[FactorInteger[8^n - 1][[-1, 1]], {n, 40}]
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PROG
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(Magma) [Maximum(PrimeDivisors(8^n-1)): n in [1..40]];
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CROSSREFS
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Cf. similar sequences listed in A274906.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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a(403)-a(500) in b-file from Max Alekseyev, Apr 25 2022, Sep 11 2022, Dec 05 2022, Feb 25 2023
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STATUS
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approved
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