cp's OEIS Frontend

A240507 Numbers k such that 6^k - 5^k - 4^k - 3^k - 2^k - 1 is prime.

%I A240507 #30 May 25 2025 02:00:03
%S A240507 4,6,12,16,34,48,68,384,1080,5892,9816,34008,50034,128256
%N A240507 Numbers k such that 6^k - 5^k - 4^k - 3^k - 2^k - 1 is prime.
%C A240507 a(11) > 7500.
%C A240507 All terms are even. - _Jon Perry_, Apr 12 2014
%e A240507 6^4 - 5^4 - 4^4 - 3^4 - 2^4 - 1 = 317 is prime. Thus, 4 is a term.
%o A240507 (PARI) for(n=1,7500,if(ispseudoprime(6^n-5^n-4^n-3^n-2^n-1),print(n)))
%o A240507 (Python)
%o A240507 from sympy import isprime
%o A240507 def afind(limit, k0=1):
%o A240507     pow6, pow5, pow4, pow3, pow2 = 6**k0, 5**k0, 4**k0, 3**k0, 2**k0
%o A240507     for k in range(k0, limit+1):
%o A240507         if isprime(pow6 - pow5 - pow4 - pow3 - pow2 - 1): print(k, end=", ")
%o A240507         pow6 *= 6; pow5 *= 5; pow4 *= 4; pow3 *= 3; pow2 *= 2
%o A240507 afind(1100) # _Michael S. Branicky_, Aug 21 2021
%Y A240507 Cf. A147977.
%Y A240507 Cf. A000043, A240503.
%K A240507 nonn,more
%O A240507 1,1
%A A240507 _Derek Orr_, Apr 06 2014
%E A240507 a(11) from _Michael S. Branicky_, Aug 21 2021
%E A240507 a(12)-a(13) from _Michael S. Branicky_, Jul 05 2024
%E A240507 a(14) from _Michael S. Branicky_, May 24 2025