A359685 Greatest prime dividing 2^n + n.

3, 3, 11, 5, 37, 7, 5, 11, 521, 47, 71, 79, 547, 911, 32783, 241, 307, 6899, 24967, 87383, 457, 4799, 270601, 7109, 3728273, 12497, 1201, 100613, 2017, 17318417, 859, 87211, 47491, 8589934609, 195329, 1483453, 320370521, 8191129, 549755813927, 478881371

Offset: 1

Author

Philippe Deléham, Jan 11 2023

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..406

Crossrefs

Cf. A000040, A006127, A006530.

Programs

Maple

a:= n-> max(numtheory[factorset](2^n+n)):
seq(a(n), n=1..40);  # Alois P. Heinz, Jan 11 2023

Mathematica

a[n_] := FactorInteger[2^n + n][[-1, 1]]; Array[a, 40] (* Amiram Eldar, Mar 30 2023 *)

PARI

a(n) = vecmax(factor(2^n+n)[,1]); \\ Michel Marcus, Jan 11 2023

Python

from sympy import primefactors
def A359685(n): return max(primefactors((1<Chai Wah Wu, Jan 11 2023

Formula

a(n) = A006530(A006127(n)).