A023509 Greatest prime divisor of prime(n) + 1.

3, 2, 3, 2, 3, 7, 3, 5, 3, 5, 2, 19, 7, 11, 3, 3, 5, 31, 17, 3, 37, 5, 7, 5, 7, 17, 13, 3, 11, 19, 2, 11, 23, 7, 5, 19, 79, 41, 7, 29, 5, 13, 3, 97, 11, 5, 53, 7, 19, 23, 13, 5, 11, 7, 43, 11, 5, 17, 139, 47, 71, 7, 11, 13, 157, 53, 83, 13, 29, 7, 59, 5, 23, 17, 19, 3, 13

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

A005382 is the records subsequence of this sequence. - David James Sycamore, May 05 2025

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006530, A008864, A005382.

Programs

Mathematica

Table[FactorInteger[Prime[n] + 1][[-1, 1]], {n, 100}]

PARI

A023509(n) = {local(f);f=factor(prime(n)+1);f[matsize(f)[1],1]} \\ Michael B. Porter, Feb 02 2010

Formula

a(n) = A006530(A008864(n)). - R. J. Mathar, Feb 06 2019