A023590 Greatest prime divisor of 2*prime(n)+1.

5, 7, 11, 5, 23, 3, 7, 13, 47, 59, 7, 5, 83, 29, 19, 107, 17, 41, 5, 13, 7, 53, 167, 179, 13, 29, 23, 43, 73, 227, 17, 263, 11, 31, 23, 101, 7, 109, 67, 347, 359, 11, 383, 43, 79, 19, 47, 149, 13, 17, 467, 479, 23, 503, 103, 31, 11, 181, 37, 563, 7, 587, 41, 89

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006530, A072055.

Programs

Mathematica

Table[FactorInteger[2Prime[n]+1][[-1,1]],{n,70}] (* Harvey P. Dale, Jun 22 2013 *)

PARI

a(n) = vecmax(factor(2*prime(n)+1)[,1]); \\ Michel Marcus, Aug 08 2020

Formula

a(n) = A006530(A072055(n)). - Amiram Eldar, Aug 08 2020