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A128025
Numbers k such that (8^k - 3^k)/5 is prime.
29
2, 3, 7, 19, 31, 67, 89, 9227, 43891, 854149
OFFSET
1,1
COMMENTS
All terms are primes.
Verified the first 8 terms in sequence. Also, the next number in the sequence, if one exists is > 43691. - Robert Price, Mar 16 2010
a(10) > 10^5. - Robert Price, Jul 27 2011
a(11) > 10^6. - Jon Grantham, Jul 29 2023
LINKS
Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.
MATHEMATICA
k=5; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]
PROG
(PARI) is(n)=isprime((8^n-3^n)/5) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. A028491 = numbers n such that (3^n - 1)/2 is prime. Cf. A057468 = numbers n such that 3^n - 2^n is prime. Cf. A059801 = numbers n such that 4^n - 3^n is prime. Cf. A121877 = numbers n such that (5^n - 3^n)/2 is a prime. Cf. A128024, A128026, A128027, A128028, A128029, A128030, A128031, A128032.
Sequence in context: A195354 A244638 A113165 * A092064 A152609 A298943
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 11 2007
EXTENSIONS
9227 from Farideh Firoozbakht, Apr 08 2007
a(9) from Robert Price, Jul 27 2011
a(10) from Jon Grantham, Jul 29 2023
STATUS
approved