A071190 - OEIS

A071190

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

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