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A071190
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Greatest prime factor of sum of divisors of n, for n >= 2; a(1) = 1.
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11
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1, 3, 2, 7, 3, 3, 2, 5, 13, 3, 3, 7, 7, 3, 3, 31, 3, 13, 5, 7, 2, 3, 3, 5, 31, 7, 5, 7, 5, 3, 2, 7, 3, 3, 3, 13, 19, 5, 7, 5, 7, 3, 11, 7, 13, 3, 3, 31, 19, 31, 3, 7, 3, 5, 3, 5, 5, 5, 5, 7, 31, 3, 13, 127, 7, 3, 17, 7, 3, 3, 3, 13, 37, 19, 31, 7, 3, 7, 5, 31
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OFFSET
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1,2
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COMMENTS
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a(n) is the greatest noncomposite factor of the sum of divisors of n. (Cf. A008578.) - Omar E. Pol, Feb 11 2018
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LINKS
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FORMULA
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MATHEMATICA
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Table[FactorInteger[DivisorSigma[1, n]][[-1, 1]], {n, 80}] (* Harvey P. Dale, Nov 18 2014 *)
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PROG
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(PARI) a(n) = if (n==1, 1, my(f = factor(sigma(n))); f[#f~, 1]); \\ Michel Marcus, Sep 21 2014
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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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