A071216 a(n) is the largest prime factor of prime(n) + prime(n+1).

5, 2, 3, 3, 3, 5, 3, 7, 13, 5, 17, 13, 7, 5, 5, 7, 5, 2, 23, 3, 19, 3, 43, 31, 11, 17, 7, 3, 37, 5, 43, 67, 23, 3, 5, 11, 5, 11, 17, 11, 5, 31, 3, 13, 11, 41, 31, 5, 19, 11, 59, 5, 41, 127, 13, 19, 5, 137, 31, 47, 3, 5, 103, 13, 7, 3, 167, 19, 29, 13, 89, 11, 37, 47, 127, 193, 131, 19

Offset: 1

Author

Labos Elemer, May 17 2002

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A006530, A001043, A071215.

Programs

Mathematica

pf[x_] := Part[Reverse[Flatten[FactorInteger[x]]],2]; Table[pf[Prime[w+1]+Prime[w]], {w,1,128}]

PARI

a(n) = vecmax(factor(prime(n)+prime(n+1))[,1]); \\ Michel Marcus, Aug 29 2019

Formula

a(n) = A006530(A001043(n)).