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 A128347 Numbers k such that (11^k - 5^k)/6 is prime. 26

%I

%S 5,41,149,229,263,739,3457,20269,98221

%N Numbers k such that (11^k - 5^k)/6 is prime.

%C All terms are primes.

%C a(10) > 10^5. - _Robert Price_, Jan 24 2013

%t k=11; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

%o (PARI) is(n)=isprime((11^n-5^n)/6) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y Cf. A062572, A128344, A128345, A128346, A128348, 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(7)-a(9) from _Robert Price_, Jan 24 2013

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Last modified June 17 15:28 EDT 2019. Contains 324194 sequences. (Running on oeis4.)