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 A128348 Numbers n such that (12^n - 5^n)/7 is prime. 20

%I

%S 2,3,31,41,53,101,421,1259,4721,45259

%N Numbers n such that (12^n - 5^n)/7 is prime.

%C All terms are primes.

%C Primality of the primes formed by a(8) and a(9) were certified by Primo. - _Ray G. Opao_, Jul 01 2012

%C a(11) > 10^5. - _Robert Price_, Mar 02 2013

%t k=12; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

%o (PARI) is(n)=isprime((12^n-5^n)/7) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y Cf. A062572, A128344, A128345, A128346, A128347, A128349, A128350, A128351, A128352, A128353, A128354. Cf. A004061, A082182, A121877, A059802. Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, A128339, A128340, A128341, A128342.

%K hard,more,nonn

%O 1,1

%A _Alexander Adamchuk_, Feb 27 2007

%E a(8) and a(9) from _Ray G. Opao_, Jul 01 2012

%E a(10) from _Robert Price_, Mar 02 2013

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Last modified February 24 10:37 EST 2020. Contains 332209 sequences. (Running on oeis4.)