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A128346 Numbers k such that (9^k - 5^k)/4 is prime. 20
3, 11, 17, 173, 839, 971, 40867, 45821, 147503 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
All terms are primes.
a(9) > 10^5. - Robert Price, Jan 19 2013
a(10) > 10^6. - Jon Grantham, Jul 29 2023
LINKS
Table of n, a(n) for n=1..9.
Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.
MATHEMATICA
k=9; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}]
PROG
(PARI) is(n)=isprime((9^n-5^n)/4) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. A062572, A128344, A128345, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354.
Cf. A004061, A082182, A121877, A059802.
Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, A128339, A128340, A128341, A128342.
Sequence in context: A072982 A124787 A080306 * A128031 A194128 A127995
Adjacent sequences: A128343 A128344 A128345 * A128347 A128348 A128349
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 27 2007
EXTENSIONS
a(7)-a(8) from Robert Price, Jan 19 2013
a(8) corrected by Robert Price, Jan 20 2013
a(9) from Jon Grantham, Jul 29 2023
STATUS
approved

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Last modified August 1 11:22 EDT 2024. Contains 374817 sequences. (Running on oeis4.)