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%I #19 Jul 06 2024 13:52:30
%S 4,8,72,396,4428,63152
%N Numbers k such that 5^k - 4^k - 3^k - 2^k - 1 is prime.
%C a(7) > 70000. - _Giovanni Resta_, Apr 09 2014
%C a(7) > 110000. - _Michael S. Branicky_, Jul 06 2024
%e 5^4-4^4-3^4-2^4-1 = 271 is prime. Thus, 4 is a term of this sequence.
%o (PARI) for(n=1,7500,if(ispseudoprime(5^n-4^n-3^n-2^n-1),print(n)))
%Y Cf. A000043, A240507.
%K nonn,more
%O 1,1
%A _Derek Orr_, Apr 06 2014
%E a(6) from _Giovanni Resta_, Apr 09 2014