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%I #34 Sep 08 2022 08:45:57
%S 2,3,6,9,21,25,33,49,54,133,245,255,318,1023,1486,3334,6821,8555,
%T 11605,42502,44409,90291,92511,140303
%N Numbers n such that 7^n - 6 is prime.
%C a(14)=1023 and a(15)=1486 correspond to BPSW strong probable primes (passing PARI's ispseudoprime()). - _Joerg Arndt_, Jun 06 2011
%C a(25) > 2*10^5. - _Robert Price_, Nov 14 2014
%p A191469:=n->`if`(isprime(7^n-6),n,NULL): seq(A191469(n), n=1..10^3); # _Wesley Ivan Hurt_, Nov 14 2014
%t Select[Range[1,5000],PrimeQ[7^#-6]&] (* _Vincenzo Librandi_, Aug 05 2012 *)
%o (Magma) [n: n in [1..1000]| IsPrime(7^n-6)]
%o (PARI) for(n=1, 10^6, if(isprime(7^n-6), print1(n, ", ")))
%Y Cf. A014224, A059266, A059613, A059614, A095714, A177093.
%Y Cf. A236371, A217131, A191469, A090669, A096305, A217130, A217132, A152213.
%K nonn,hard,more
%O 1,1
%A _Vincenzo Librandi_, Jun 06 2011
%E a(17)-a(23) from _Robert Price_, Jan 24 2014
%E a(24) from _Robert Price_, Nov 14 2014
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