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A240507
Numbers k such that 6^k - 5^k - 4^k - 3^k - 2^k - 1 is prime.
3
4, 6, 12, 16, 34, 48, 68, 384, 1080, 5892, 9816, 34008, 50034
OFFSET
1,1
COMMENTS
a(11) > 7500.
All terms are even. - Jon Perry, Apr 12 2014
EXAMPLE
6^4 - 5^4 - 4^4 - 3^4 - 2^4 - 1 = 317 is prime. Thus, 4 is a term.
PROG
(PARI) for(n=1, 7500, if(ispseudoprime(6^n-5^n-4^n-3^n-2^n-1), print(n)))
(Python)
from sympy import isprime
def afind(limit, k0=1):
pow6, pow5, pow4, pow3, pow2 = 6**k0, 5**k0, 4**k0, 3**k0, 2**k0
for k in range(k0, limit+1):
if isprime(pow6 - pow5 - pow4 - pow3 - pow2 - 1): print(k, end=", ")
pow6 *= 6; pow5 *= 5; pow4 *= 4; pow3 *= 3; pow2 *= 2
afind(1100) # Michael S. Branicky, Aug 21 2021
CROSSREFS
Cf. A147977.
Sequence in context: A327479 A139056 A152519 * A022802 A301166 A310599
KEYWORD
nonn,more
AUTHOR
Derek Orr, Apr 06 2014
EXTENSIONS
a(11) from Michael S. Branicky, Aug 21 2021
a(12)-a(13) from Michael S. Branicky, Jul 05 2024
STATUS
approved