A078551 - OEIS

%I #9 Aug 01 2019 11:32:21

%S 5,5,7,13,5,5,17,13,13,61,7,17,5,13,31,29,13,181,13,5,61,53,17,31,17,

%T 41,7,421,13,37,13,61,29,13,13,137,181,17,17,29,5,37,61,13,53,17,31,

%U 43,31,29,17,281,41,61,17,181,421,1741,13,1861,37,13,127,17,61,449,29,53

%N Largest prime dividing sigma(2,n).

%H Amiram Eldar, <a href="/A078551/b078551.txt">Table of n, a(n) for n = 2..10000</a>

%F a(n) = A006530(A001157(n)).

%t gpf[n_] := FactorInteger[n][[-1, 1]]; a[n_] := gpf[DivisorSigma[2, n]]; Array[a, 70, 2] (* _Amiram Eldar_, Aug 01 2019 *)

%Y Cf. A006530, A001157-A001160, A071190.

%K nonn

%O 2,1

%A _Labos Elemer_, Dec 05 2002