%I
%S 1,2,6,9,12,14,26,33,44,54,126,141,830,2436,3534,3846,4152,4460,4974,
%T 13160,13200,13832
%N Numbers k such that 7^k + 2 is semiprime.
%C Or, (7^n + 2)/3 is prime.
%e 12 is a term because 7^12 + 2 = 13841287203 = 3*4613762401 and 4613762401 is prime.
%t Select[Range[2100], PrimeQ[(7^# + 2)/3] &] (* _Stefan Steinerberger_, Jul 22 2006 *)
%K nonn,more
%O 1,2
%A _Zak Seidov_, Jun 13 2006
%E More terms from _Stefan Steinerberger_ and _Joshua Zucker_, Jun 21 2006
%E a(14) from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008
%E a(15)a(22) from _Sean A. Irvine_, Dec 16 2009
