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 A128342 Numbers k such that (13^k + 5^k)/18 is prime. 23
 13, 19, 31, 359, 487, 757, 761, 1667, 2551, 3167, 6829 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are primes. No other terms below 23600. - Max Alekseyev, Feb 01 2010 a(12) > 10^5. - Robert Price, Apr 30 2013 LINKS MATHEMATICA k=13; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 100}] PROG (PARI) is(n)=isprime((13^n+5^n)/18) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, A128339, A128340, A128341, A128343. Cf. A004061, A082182, A121877, A059802. Cf. A062572, A128344, A128345, A128346, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354. Sequence in context: A023252 A279426 A241120 * A154076 A275660 A088186 Adjacent sequences:  A128339 A128340 A128341 * A128343 A128344 A128345 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 27 2007 EXTENSIONS Four more terms from Max Alekseyev, Feb 01 2010 STATUS approved

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Last modified February 23 23:59 EST 2020. Contains 332195 sequences. (Running on oeis4.)