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A274903
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Largest prime factor of 4^n + 1.
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16
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2, 5, 17, 13, 257, 41, 241, 113, 65537, 109, 61681, 2113, 673, 1613, 15790321, 1321, 6700417, 26317, 38737, 525313, 4278255361, 14449, 2931542417, 30269, 22253377, 268501, 308761441, 279073, 54410972897, 536903681, 4562284561, 384773, 67280421310721
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OFFSET
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0,1
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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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4^3 + 1 = 65 = 5*13, so a(3) = 13.
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MATHEMATICA
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Table[FactorInteger[4^n + 1][[-1, 1]], {n, 0, 30}]
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PROG
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(Magma) [Maximum(PrimeDivisors(4^n+1)): n in [0..35]];
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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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a(532)-a(561) in b-file from Max Alekseyev, Apr 25 2022, Apr 15 2023
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STATUS
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approved
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