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 A138051 Numbers k such that 27^k + 2 is prime. 7
 0, 1, 5, 8, 12, 21, 41, 42, 81, 105, 121, 377, 501, 2401, 14597, 35381, 59476, 120536 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS All terms are the exact thirds of terms of A051783 that are divisible by 3. Conjecture: 3^3^n+2 does not meet anti Fermat's conjecture. - Vincenzo Librandi, Aug 01 2010 LINKS Henri & Renaud Lifchitz, PRP Records. MATHEMATICA Do[ f = 27^n + 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n, 1, 2500} ] PROG (PARI) is(n)=ispseudoprime(27^n+2) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A051783 = Numbers n such that 3^n + 2 is prime. Cf. A087885 = Numbers n such that 5^n + 2 is prime. Cf. A090649, A109076, A113480, A138048, A138049, A138050, A087886, A113481. Cf. A176495. Sequence in context: A115072 A114644 A314419 * A026279 A260966 A338547 Adjacent sequences:  A138048 A138049 A138050 * A138052 A138053 A138054 KEYWORD nonn AUTHOR Alexander Adamchuk, Mar 02 2008 EXTENSIONS a(15)-a(17) from A051783 by Ray Chandler, Aug 06 2011 a(18) from Robert Price, May 12 2019 STATUS approved

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Last modified April 14 06:59 EDT 2021. Contains 342946 sequences. (Running on oeis4.)