A078554 Largest prime dividing sigma(5,n).

11, 61, 151, 521, 61, 191, 41, 4561, 521, 13421, 151, 2411, 191, 521, 1801, 101, 4561, 2251, 521, 191, 13421, 211, 61, 1741, 2411, 1181, 191, 401, 521, 21821, 331, 13421, 101, 521, 4561, 1824841, 2251, 2411, 521, 4111, 191, 3341101, 13421, 4561, 211

Offset: 2

Author

Labos Elemer, Dec 05 2002

Keywords

• nonn

Examples

			Observe nontrivial frequent occurrence of several primes like 61,191,521,4561, etc.
		

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[5, n]]; Array[a, 50, 2] (* Amiram Eldar, Aug 01 2019 *)
FactorInteger[#][[-1,1]]&/@DivisorSigma[5,Range[2,50]] (* Harvey P. Dale, Feb 02 2025 *)

Formula

a(n) = A006530(A001160(n)).