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A274909
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Largest prime factor of 9^n - 1.
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13
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2, 5, 13, 41, 61, 73, 1093, 193, 757, 1181, 3851, 6481, 797161, 16493, 4561, 21523361, 34511, 530713, 363889, 42521761, 368089, 570461, 23535794707, 6481, 22996651, 4795973261, 19927, 647753, 20381027, 47763361, 22434744889, 926510094425921, 2413941289
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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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9^4 - 1 = 6560 = 2^5*5*41, so a(4) = 41.
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MATHEMATICA
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Table[FactorInteger[9^n-1][[-1, 1]], {n, 40}]
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PROG
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(Magma) [Maximum(PrimeDivisors(9^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(331)-a(691) in b-file from Max Alekseyev, May 22 2022, Jul 25 2023
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STATUS
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approved
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