A055385 - OEIS

%I #35 Jul 22 2019 17:28:57

%S 2,5,2,257,2,13,2,97,2,101,2,89,2,29,2,274177,2,5,2,148721,2,5,2,17,2,

%T 53,2,449,2,17,2,641,2,13,2,17,2,5,2,17,2,5,2,41,2,29,2,769,2,41,2,89,

%U 2,13,2,17,2,5,2,17,2,5,2,59649589127497217,2,37,2,41,2,13,2,97,2,149

%N Smallest prime factor of n^n + 1.

%C If we use the commonly accepted convention that 0^0 = 1, then a(0) = 2. - Chai Wah Wu, Jul 22 2019

%D C. Stanley Ogilvy and John T. Anderson, Excursions in Number Theory. Dover. New York: 1988. Page 82.

%H Seiichi Manyama, <a href="/A055385/b055385.txt">Table of n, a(n) for n = 1..500</a>

%e 4^4 + 1 = 257 prime, so a(4) = 257;

%e 6^6 + 1 = 13 * 37 * 97, so a(6) = 13.

%t Table[FactorInteger[n^n + 1][[1, 1]], {n, 74}] (* _Vincenzo Librandi_, Jul 23 2013 *)

%o (PARI) a(n) =  {if (n % 2, return (2)); return (factor(n^n + 1)[1, 1]);} \\ _Michel Marcus_, Jul 23 2013

%Y Cf. A014566, A055386.

%K nonn

%O 1,1

%A _Walter Nissen_, Jun 24 2000