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Greatest prime divisor of 2*prime(n)+1.
4

%I #12 Aug 08 2020 11:29:34

%S 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,

%T 29,23,43,73,227,17,263,11,31,23,101,7,109,67,347,359,11,383,43,79,19,

%U 47,149,13,17,467,479,23,503,103,31,11,181,37,563,7,587,41,89

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

%H Amiram Eldar, <a href="/A023590/b023590.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A006530(A072055(n)). - _Amiram Eldar_, Aug 08 2020

%t Table[FactorInteger[2Prime[n]+1][[-1,1]],{n,70}] (* _Harvey P. Dale_, Jun 22 2013 *)

%o (PARI) a(n) = vecmax(factor(2*prime(n)+1)[,1]); \\ _Michel Marcus_, Aug 08 2020

%Y Cf. A006530, A072055.

%K nonn

%O 1,1

%A _Clark Kimberling_