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%I #33 Jul 04 2021 07:52:25
%S 2,5,11,13,23,61,83,421,1039,1511,31237,60413,113177,135647,258413
%N Numbers k such that 6^k - 5^k is prime.
%C The 809- and 1176-digit numbers associated with the terms 1039 and 1511 have been certified prime with Primo. - _Rick L. Shepherd_, Nov 15 2002
%e 2 is in the sequence because 6^2 - 5^2 = 36 - 25 = 11, which is prime.
%e 3 is not in the sequence because 6^3 - 5^3 = 216 - 125 = 91 = 7 * 13, which is not prime.
%t Select[Range[1000], PrimeQ[6^# - 5^#] &] (* _Alonso del Arte_, Sep 04 2013 *)
%o (PARI) forprime(p=2,1e4,if(ispseudoprime(6^n-5^n),print1(p", "))) \\ _Charles R Greathouse IV_, Jun 10 2011
%Y Cf. A000043, A057468, A059801, A059802, A062573-A062666.
%K nonn,hard,more
%O 1,1
%A _Mike Oakes_, May 18 2001, May 19 2001
%E Edited by _T. D. Noe_, Oct 30 2008
%E Two more terms (31237 and 60413) found by Predrag Minovic in 2004 corresponding to probable primes with 24308 and 47011 digits. _Jean-Louis Charton_, Oct 06 2010
%E Two more terms (113177 and 135647) found by Jean-Louis Charton in 2009 corresponding to probable primes with 88069 and 105554 digits. _Jean-Louis Charton_, Oct 13 2010
%E a(15) from _Jean-Louis Charton_, Apr 08 2013
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