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 A079906 Numbers k such that 5*6^k -1 is prime. 15
 1, 2, 6, 7, 11, 23, 33, 48, 68, 79, 116, 151, 205, 1016, 1332, 1448, 3481, 3566, 3665, 11233, 13363, 29166, 44358, 58530, 191706, 386450, 605168, 616879 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(29) > 618,000 - Karsten Bonath, Nov 04 2019 REFERENCES R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3. LINKS H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17. MATHEMATICA Do[ If[ PrimeQ[5*6^n - 1], Print[n]], {n, 1, 5000}] PROG (PARI) for(n=1, 2000, if(isprime(5*6^n-1), print1(n, ", "))) CROSSREFS Cf. A003307, A002235, A046865, A046866, A001771, A005541, A056725, A046867, A079907, A247260. Sequence in context: A241720 A224082 A051678 * A226814 A233419 A189327 Adjacent sequences:  A079903 A079904 A079905 * A079907 A079908 A079909 KEYWORD nonn,hard,more AUTHOR Robert G. Wilson v, Jan 16 2003 EXTENSIONS a(20)-a(24) from Donovan Johnson, Nov 26 2008 a(25) from Robert Price, Jan 23 2016 a(26) from Karsten Bonath, Jul 01 2019 a(27) from Karsten Bonath, Oct 29 2019 a(28) from Karsten Bonath, Nov 04 2019 STATUS approved

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Last modified October 20 19:28 EDT 2020. Contains 337909 sequences. (Running on oeis4.)