%I #11 Oct 29 2023 09:47:10

%S 11,37,11,41,7,239,11,37,11,21649,7,53,11,31,11,2071723,7,

%T 1111111111111111111,11,37,11,11111111111111111111111,7,41,11,37,11,

%U 3191,7,2791,11,37,11,41,7,2028119,11,37,11,83,7,173,11,31,11,35121409,7,239,11,37,11,107

%N a(n) is the least prime factor > 3 of 10^n - 1.

%e a(2) = 11 because 99 = 3^2 * 11 = 3^A366922(2) * A003020(2).

%e a(9) = 37 because 10^9 - 1 = 3^4 * 37 * 333667 = 3^A366922(9) * 37 * A003020(9).

%o (PARI) a366921(n) = factor(10^n-1)[2,1]

%Y Cf. A002283, A003020, A102347, A366922.

%K nonn

%O 2,1

%A _Hugo Pfoertner_, Oct 28 2023