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A274906
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Largest prime factor of 4^n - 1.
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15
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3, 5, 7, 17, 31, 13, 127, 257, 73, 41, 683, 241, 8191, 127, 331, 65537, 131071, 109, 524287, 61681, 5419, 2113, 2796203, 673, 4051, 8191, 262657, 15790321, 3033169, 1321, 2147483647, 6700417, 599479, 131071, 122921, 38737, 616318177, 525313, 22366891
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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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4^7 - 1 = 16383 = 3*43*127, so a(7) = 127
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MATHEMATICA
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Table[FactorInteger[4^n - 1][[-1, 1]], {n, 40}]
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PROG
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(Magma) [Maximum(PrimeDivisors(4^n-1)): n in [1..40]];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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