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 A071190 Greatest prime factor of sum of divisors of n, for n >= 2; a(1) = 1. 10

%I

%S 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,

%T 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,

%U 13,127,7,3,17,7,3,3,3,13,37,19,31,7,3,7,5,31

%N Greatest prime factor of sum of divisors of n, for n >= 2; a(1) = 1.

%C a(n) is the greatest noncomposite factor of the sum of divisors of n. (Cf. A008578.) - _Omar E. Pol_, Feb 11 2018

%H Antti Karttunen, <a href="/A071190/b071190.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A006530(A000203(n)).

%t Table[FactorInteger[DivisorSigma[1,n]][[-1,1]],{n,80}] (* _Harvey P. Dale_, Nov 18 2014 *)

%o (PARI) a(n) = if (n==1, 1, my(f = factor(sigma(n))); f[#f~,1]); \\ _Michel Marcus_, Sep 21 2014

%Y Cf. A000203, A006530, A071188, A071189.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, May 15 2002

%E Name clarified by _David A. Corneth_ and _Omar E. Pol_, Feb 11 2018

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Last modified August 10 16:56 EDT 2020. Contains 336381 sequences. (Running on oeis4.)