A208399 - OEIS

%I #17 Sep 11 2012 14:11:50

%S 17,73,65537,41,1297,13564461457,193,6481,1676321,251857,97,380329,

%T 1009,33601,59649589127497217,137,11019855601,1217,76001,3697,881,

%U 428353,193,4001,8737,530713,7841,7830180737690995967783421720386927955722346842901104163321719186184830340945285361

%N Smallest prime factor of (n^n)^2 + 1 having the form k*n+1.

%C The corresponding k are in A208400.

%e a(3) = 73 because (3^3)^2 + 1 = 2*5*73 and the smallest prime divisor of the form k*n+1 is 73 = 24*3+1.

%t Table[p=First/@FactorInteger[(n^n)^2+1]; Select[p, Mod[#1, n] == 1 &, 1][[1]], {n, 2, 20}]

%Y Cf. A208400.

%K nonn

%O 2,1

%A _Michel Lagneau_, Feb 27 2012