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 A128346 Numbers n such that (9^n - 5^n)/4 is prime. 20
 3, 11, 17, 173, 839, 971, 40867, 45821 (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 LINKS 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: A124787 A080306 A036448 * 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 STATUS approved

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Last modified February 24 00:19 EST 2020. Contains 332195 sequences. (Running on oeis4.)