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

%I #15 Mar 05 2020 03:24:34

%S 5,7,11,3,23,3,5,3,47,59,3,3,83,3,5,107,7,3,3,11,3,3,167,179,3,7,3,5,

%T 3,227,3,263,5,3,13,3,3,3,5,347,359,3,383,3,5,3,3,3,5,3,467,479,3,503,

%U 5,17,7,3,3,563,3,587,3,7,3,5,3,3,5,3,7,719,3,3,3,13,19,3,11,3

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

%H Amiram Eldar, <a href="/A023592/b023592.txt">Table of n, a(n) for n = 1..10000</a>

%t Table[FactorInteger[2*Prime[n] + 1][[1, 1]], {n, 1, 80}] (* _Amiram Eldar_, Mar 05 2020 *)

%o (PARI) a(n) = factor(2*prime(n)+1)[1, 1]; \\ _Michel Marcus_, Oct 02 2013

%Y Except for first term, same as A094460.

%K nonn

%O 1,1

%A _Clark Kimberling_