Search: id:A119720
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%I A119720
%S A119720 1,2,6,9,12,14,26,33,44,54,126,141,830,2436
%N A119720 Numbers n such that 7^n + 2 is semiprime.
%C A119720 Or, (7^n+2)/3 is prime.
%C A119720 Next term is bigger than 2100.
%e A119720 12 is OK because 7^12+2=13841287203=3*4613762401 and 4613762401 is prime.
%t A119720 Select[Range[2100], PrimeQ[(7^# + 2)/3] &] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), 
               Jul 22 2006
%Y A119720 Sequence in context: A026348 A032713 A086939 this_sequence A000134 A120701 
               A112870
%Y A119720 Adjacent sequences: A119717 A119718 A119719 this_sequence A119721 A119722 
               A119723
%K A119720 more,nonn,less
%O A119720 1,2
%A A119720 Zak Seidov (zakseidov(AT)yahoo.com), Jun 13 2006
%E A119720 More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com) 
               and Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jun 21 2006
%E A119720 a(14) from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008

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