A078551 Largest prime dividing sigma(2,n).

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, 41, 7, 421, 13, 37, 13, 61, 29, 13, 13, 137, 181, 17, 17, 29, 5, 37, 61, 13, 53, 17, 31, 43, 31, 29, 17, 281, 41, 61, 17, 181, 421, 1741, 13, 1861, 37, 13, 127, 17, 61, 449, 29, 53

Offset: 2

Author

Labos Elemer, Dec 05 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A006530, A001157-A001160, A071190.

Programs

Mathematica

gpf[n_] := FactorInteger[n][[-1, 1]]; a[n_] := gpf[DivisorSigma[2, n]]; Array[a, 70, 2] (* Amiram Eldar, Aug 01 2019 *)

Formula

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