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A128337 Numbers n such that (7^n + 5^n)/12 is prime. 19


%S 11,31,173,271,547,1823,2111,5519,7793,22963,41077,49739

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

%C All terms are primes.

%C a(13) > 10^5. - _Robert Price_, Nov 20 2012

%t k=7; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

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

%Y Cf. A057171, A082387, A122853, A128335, A128336, A128338, A128339, A128340, A128341, A128342, A128343. Cf. A004061, A082182, A121877, A059802. Cf. A062572, A128344, A128345, A128346, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354.

%K hard,more,nonn

%O 1,1

%A _Alexander Adamchuk_, Feb 27 2007

%E a(6)-a(12) from _Robert Price_, Nov 20 2012

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Last modified January 21 21:30 EST 2020. Contains 331128 sequences. (Running on oeis4.)