

A071190


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


10



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

1,2


COMMENTS

a(n) is the greatest noncomposite factor of the sum of divisors of n. (Cf. A008578.)  Omar E. Pol, Feb 11 2018


LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000


FORMULA

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


MATHEMATICA

Table[FactorInteger[DivisorSigma[1, n]][[1, 1]], {n, 80}] (* Harvey P. Dale, Nov 18 2014 *)


PROG

(PARI) a(n) = if (n==1, 1, my(f = factor(sigma(n))); f[#f~, 1]); \\ Michel Marcus, Sep 21 2014


CROSSREFS

Cf. A000203, A006530, A071188, A071189.
Sequence in context: A099378 A182885 A182891 * A295314 A057020 A257322
Adjacent sequences: A071187 A071188 A071189 * A071191 A071192 A071193


KEYWORD

nonn


AUTHOR

Reinhard Zumkeller, May 15 2002


EXTENSIONS

Name clarified by David A. Corneth and Omar E. Pol, Feb 11 2018


STATUS

approved



